first the straight answer. Yes you can have more than one social presence to help you earn income.
The difficult part is saying how much time you must spend on any one of your social media areas.
I have been writing, blogging etc. for over five years now. I can spend eight hours per day working on various projects for one outlet or another. I manage this alongside working a thirty hours per week job as well and own an online bookstore.
I built up on the time that I invest over years. It all takes time and work I did in 2009 still pays me residual income, so non of the work is wasted.
If you are looking into areas to invest time, Wiley and Sons print a series of books about Social Media, Marketing, Blogging and Online business. Wiley are more famous for tthe "Dummies" series of books which are good resources, but also print the "One Hour a Day" series which are another rich resource that I use.
Keep things under control though, work on one project at a time, it can take six months to a year to build a sufficient presence. Limiting yourself to one or two sites at first means that you don't overeach yourself too soon. Once online you really need to stay online. Too much too soon means that some of your sites may get dropped by you which is more damaging than never having created a presence.
Hope this answer might be helpful to you.