I'd agree with Sigg that purchase price would include installation, with one caveat, no standard discount. And if for some reason the PC's have picked up the hardware and are looking for installation that'll cost (book 2) 10% the value of the hardware (the standard discount value).
The hardware would be available only at a class A or B starport, or any Scout or Navy base imo. Installation would be no problem for even a class C starport (treating as repair) but not possible below that.
PC self installation, tricky, lots of variables. Probably easiest to say no.
Times. A day to change a single weapon in a turret and a day to install or remove a turret. So for a new triple turret with weapons, 4 days. Or to swap a single weapon for a different type in an already installed turret, 4 days (1 day to remove turret, 1 day to remove old weapon, 1 day to install new weapon, and 1 day to reinstall turret). Multiple turrets could be installed at the same time by different teams if available*. But there'd be no other business possible on the ship during that time and the crew would have to find other accomodations.
* 8+ roll for an extra team, DM +3 for class A, DM +0 for class B, DM -2 for class C, DM +5 for Navy base, DM +2 for Scout base; continue rolling till you miss for total teams available. Note: getting the work done on a base would be a special circumstance.
Landing fees. Those are for regular port facility access, not repair and such imo. So they have to land (book 2 cr100 for up to 6 days) then have the ship transferred to the repair yards but still keep the slip open at the regular field for when the work is done.
Just a few thoughts. And yes the open nature of your question was a good thing. I think the differences are good, not exclusive, but examples of different practices. The Solomani (fixed mounts option), civilian and paramilitary ships (book 2 and some of HG1) and Imperial Military ships (HG2). As one possible interpretation of how they are all CT.