Great points from everyone in this thread. Unfortunately, I am not able to give much assistance in regards to an upload schedule to viewer retention/interaction. But I would give a little "personal" thoughts just in case it might help you change perspective on certain topics:
THOUGHT PROCESS
I have that exact mindset you have regarding the 2-3 or daily upload. I would add that, though we have the think (yes me, too) that it will over saturate with content and prevent them from viewing, remember that viewers only view what they want. They will bypass a certain thumbnail or image that they are not interested about and go straight for certain ones (example, your fort videos are popular). I have to remind myself of this, too because let's say I play a horror game (that is not too hyped). Some may be interested due to its "rarity" and story, but others could care less cause they want to see only a specific game I played a few days ago.
Another point I always conflict with myself is the possibility of "force themselves to watch due to new channel." Basically, some only watch because we ask to help each other out and we feel obligated to keep commenting and watching to encourage one another. Not a bad thing, but realistically this will only last so long. Eventually channels grow big and lose time to watch and comment this will reveal who are your "loyal" viewers or collab buddies. So, it will be similar to saying this might be a "beginners luck" type of ordeal and we may believe we are doing good, but this is only because a feel people felt like helping just to start, but content has not changed much and they lose interest. Not sure if this is taken aggressively or demeaning. I definitely do not intend it to be like that. I am just giving a thought that I think my channel is going through due to my lack of editing and ideas to make boring content interesting.
On the bright side! As I commented in your video, this idea is fantastic and knowing your intentions behind it makes it much more fulfilling to watch and help you two out. I would even say that posting a "Results of February's daily upload experiment" video (of course with better SEO title) would be popular (well I am just that type of guy). Both as a way to showcase your hard work, but inform your viewers what you have been trying to do. This is important (to me that is), because you telling us your intentions of "promoting a certain atmosphere" is fantastic and will most likely make use feel valued as members of your atmosphere/community.
However, a critical point that comes to mind, "What atmosphere are you trying to promote?" Is this atmosphere alluring to us and are you expressing this atmosphere to us in each video? This is something I struggle with my videos when I say I want to create a community that encourages growth and promoting content. But my biggest problem is figuring out how to combine everyone's talents into a short, fun video (I have a few viewers that are singers, gamers, artists, etc and they are willing to promote, but when I gather their content I struggle a lot with figuring out how to portray them in the best light I can. Thus, I am at a loss

).
PLANNING
Again, love how you explain your process. It gives a little insight of what we should/could emulate to help ourselves progress in the future. Yes, explaining the "fort" parts and what specifically you were uploading encouraged us tremendously to visit on certain days we were interested in! As for me, I do agree that saying "subscribe or drop a like" is useless. I myself do not like how other gamers constantly stress this (if I liked their personality and content I will do so, hearing it only gives me a negative vibe because everyone knows that they can do that). Though, that is just me, it is not bad for anyone to say this. If we know you are genuine and hardworking we will be more than likely to hit the subscribe and like because you mean well and deserve it. Yes the short clip on notifications help! Mostly for new individuals new to YouTube, so always a plus to have that (again, this can be similar to the, "likes and subscribe" but hey who cares if it helps new people then go for it). Again, your scheduling and ideas to prevent monotony is great. Not much benefit from me saying it, but hey still good idea.
NEXT STEPS
First thing I wanted to note in this section was social media. One of the most important aspects to remember is that social media is not exactly a priority that should stress us out. I say this for two reasons: 1) Its a marginal increase compared to other methods; 2) Yes, I too agree its great for gathering followers, but would that time be more beneficial for increasing quality in videos? This is a double edged sword and will most likely become a flame war for what I said

(no I do not intend to start that, haha)! Main thing is, read and follow successful entrepreneurs such as Tim Ferris, Ramit Sethi, Navid Moazzez, Pat Flynn, and others. Majority will explain that social media is not the efficient for gathering clients. Take the 80/20 rule for example. "80% of your results come from 20% of your efforts." (Ramit). Most of us feel we are being "productive" when posting on social media to gain a following, but this false sense of productivity ends up providing a small benefit when instead we could have taken a different method to promoting work. Such as commenting to viewers or other channels that will reach them on a personal level and encourage networking or emailing large or smaller channels to ask if they need help that your content can assist them with. (Example: Some YouTuber's may be overwhelmed from their content, work, studies, etc and may need help from your personality, editing, or other skills to reduce the work load. This will also form a good relationship and promote their work). Yes, pros and cons, but hopefully my ranting did spark an idea?
Notes on the business cards*** "How do you know you have had a great response from this?" (again no hurt intended, just asking as a means to help out

). Let us assume that everyone who receives your card at least checks your channel. In what ways do you know they are actually viewing it, because they received the card? For me, when I visit channels and comment on their videos I purposely add lines such as, "Hey, I found your channel through..." or "[YouTuber] recommended me to view your channel..." Important to note that I specifically do this, because I feel it is a benefit for them to know and I want them to understand where their audience comes from. However, majority of others do not do this and care less. Thus, "Is there an incentive for them to add such lines when they comment or email you?" Do you write a note on the back of the card that says something similar to, "If you visit our channel from this card, please comment and say that you visited because you saw our card!" To add to that, what makes them feel like they should? I would say, your atmosphere you are creating would tie very well with this. You two have done a fantastic job in creating a community that is positive, motivated, and inspired. Could this somehow help you with understanding the demographics of the business card by having them comment like that?
Thus, ends my long rant (feedback?). Again, I never intend to irritate, troll, or cause negative emotions. I simply wrote everything that I did, because you are one of the few YouTuber Channels that I feel genuinely provide content for their community to promote a brighter, happier atmosphere. Me simply agreeing and always mentioning "good idea" has merit, but without in-depth feedback it will not provide much benefit. At the same time, maybe me writing too much would be bad too, haha

! I am still learning and hope that whatever you do progresses well. Thus, again, I will say the following:
You posting these updates is something I personally enjoy and value. Posting a results video, as well as updating everyone in a youtube video will most likely provide inspiration and motivation to your viewers. It will also give value to your viewers due in fact that you actually took the time and explained your thoughts (that because of THEM, you decided to make these changes and appreciate their support and feedback). Something like that.
Anyway, Good job for reading everything (apologies again xD) and thanks for being you (yes I say this a lot, but hey I genuinely mean it. Corny, yes. Bad thing, no

).