I would focus on your main site for right now. Make sure all of your citations(NAP - Name, address and phone number) are correct and if you don't have any add them! (Yelp, etc).

Use Google My Business, this will help get your business set up on Google (Not the serps, but Google Plus, etc)

I would start putting out quality content related to your niche and start reaching out to bloggers in your niche with blogs that have high domain and page authority.

I'm guessing the other domains you have probably don't have any domain or page authority, so I don't see those backlinks helping you at all.

Word of advice. You may find gold on those sites, but you're more likely to hurt your site when Google throws another update out and you find they used some black hat methods!

Make sure you 301 redirect your links if you change the link structure during the switch. Keep an eye on Google Webmasters for anything you might of missed.