Okay, a bunch here!
1: This is mainly a passenger liner, so the 4000 passengers would occupy the bulk of the space, even saying that a berth takes 10 tonnes, then if stripped of passenger cabins, it would convert to an extra 40,000 tonnes of cargo space. And that's not including spaces for restaurants, recreation areas, etc.
2: I don't tend to put costs unless it's up on Wookieepedia, so didn't even guess for this. But the Indulgent Class Passenger Liner which carries 1,500 passengers costs 25,500,000 credits. So maybe thereabouts?
3: They're for defence, as this would be a fairly tempting target for pirates. It would have external docks for transports, but doesn't carry any.
4: For 4,000 passengers, I'd think it would dock to a station, or land (as we've seen passenger ships do in The Mandalorian), but external airlocks would allow smaller numbers to be shuttled to and from the vessel.
5: This is a High Republic era vessel, so by the time of the Empire I'd think they'd be looking worn out and be used in the fringes of the galaxy, vessels which once were pristine and luxurious, but now are stained, worn and patched together. In their prime they'd have been used in the core systems.
6: Because it's a High Republic era vessel, I just took normal weapons and lowered the damage as it's a Civilian vessel and uses older technology than during the Galactic Civil War. In my designs lately, I tend to treat Heavy Weapons as 5D, Normal as 4D, and Light as 3D, with upgrades for number of weapons (quad, etc), so this plays off that design choice, with the Light Turbolasers scaling down to Starfighter Scale.
As usual just my thoughts, and my choices are very dependent on how I feel on any particular day. :D