I think the best thing for you to do is get your content plan in place and just go for it! (videos you can do, upload schedule, promotion plan, etc) Put AdSense in place and see what happens.
The reason I advise this is... the answers you'll get are going to be really subjective. Income is going to vary greatly depending on niche, upload schedule, etc, etc, etc. Also, what might be decent income for one may not be decent for another. (based on location, lifestyle, etc) There are people making a good living on YouTube, but nothing guarantees that you will do the same so you just have to give it a go and see.
Lastly, keep in mind there is a lag (and audit period) from the time you start getting views till the time you actually get paid, so you can't count any projections as reliable until you actually have the money in hand.
Hope that helps,
Creator X
PS It is kind of taboo to discuss income. lol Especially YouTube income as there were still TOS rules in effect last we checked.