FMIC install is an intricate project, even with a kit that's "supposed" to bolt right up. prepare to be patient and careful and accept the fact your car may be down for a good long while
WRX engine bay is incredibly tight space, already packed to the max with systems...and somehow you have to cram even more stuff in there.
the 07 nose is quite different from 02-05s. front bulkhead is lower, headlight units MUCH bulkier (harder to route stuff around) and the outer corners much more rounded off than earlier cars. All this will no doubt affect how the fmic plumbing fits. you will almost assuredly find that you'll need to sculpt (ie hack, cut, fit) here and there, and may have to relocate things like power steering reservoirs, etc.
short answer is, fmic install is NOT a shade tree, one-afternoon kind of project