With the Tech channel, it was mainly coming up with ideas and getting stuff to review, lots of emails back and forth. Also towards the end it got very repetitive hence why I only occasionally upload there now. It is currently at 4,072 subscribers.
I only just started this channel in September of last year, so I haven't been contacting companies yet as I'm only at 70 subs. The main struggle that I had recently was coming up with something that's really unique as well as more ideas for my series where I explain processes in animation. I've got answers to both of them now though and will be getting to work on videos for them after I'm finished with all this uni work (I've got reviews going up weakly in the meantime.