Blocks and CSS Grid Systems
We primarily build our sites using Bootstrap with this same technique, so here are 3 modules that will make your life a lot easier.

Block Class - add classes to blocks.

Block Group and/or Region Class - group blocks together in faux regions, add classes to regions.

Blocker - places blocks on specific pages in different regions, alternative to using the core block placement system. Really useful for site building and putting blocks on basic pages.