Heya, if you've been taken to the VIP area (the dark room with a lot of neon lights) then that is the immobile section. This is just the first size into the immobile range so it may not be as big as you'd hope/expect but we'll get there in time.
Trish's office is available at the start so no unlocking needed. You have to go to the club room (where you can dance or run drinks) and it's an option on the left side bar.
The game is made in renpy so it's just normal save/loading from there. While playing you can right click to bring up the save menu then just click one of the empty slots to save. To load it's the same thing, right click (or select load from the main menu) and select the square with the save you want to load.