For the SRV hangar, you can get those at just about every station/outpost/port that has outfitting (both orbital and planet-side). Once you mount the hangar, you will need to fill the hangar bay with a SRV (kinda like fitting a module inside a module), since the SRV is not included.
For turrets, you can use the right-hand UI panel to change the targeting of turrets in the functions tab. You can change your turrets between fire at will, selected target, and forward facing modes. The forward facing mode turns the turrets into more expensive and less effective fixed weapons, while the other two modes give your turrets the full range of motion and restrict the turret's target selection to all hostile ships or your selected target.
I don't do power play, so I can't really tell you who the best person to follow is. What I can tell you is that pledging to a power will give you some power-specific bonuses (i.e. 20% bonus to bounty value), and that powers give bonuses to the regions of space they control (i.e. 15% discount on ships and outfitting) regardless of affiliation. Also, if you get a high enough rank with a power, and have been pledged for a long enough period of time you can get access to power specific modules (Prismatic Shields, Advanced Plasma Accelerators, Pack Hounds, etc...). There a lot of stuff to cover here, so I'll leave this excellent guide
here.