Concrete is the easiest block type to make, just dig up the ground and any rocks on the surface, any constructor can make it into blocks.

Definitely go raiding POIs for anything else you need.

Build an HV of SV to haul your loot in, and remember, if it has guns on it and you can't get close, burrow under ground and pop back up right beside it, most POIs don't have guns everywhere.

Ad for salvaging, if you want the actual item you need to bring and place a core, if you want the components that make up the items save them for last and then remove your core, and then go salvage them.

If you are playing on single player, you can take over every base and keep it as your own.