I actually prefer building the dungeon first a little bit after Ellen talks about it fairly early in the game and/or shortly after Lin is fucked for the first time. Along with Lin having a story event shortly after it's built, it's a way of getting a little training for her to help prepare for a major event later on. I'll wait on the second floor until around the time that Ashley gets kicked out of school. The reason for this is because one of Ashley's Exhibition scenes in the cafe seems to be a little bit different if the twins haven't joined the hotel yet. For the bar, I just wait until everyone's moved into the second floor. The Sanctuary is best right after Lin's Contest (you'll know it when you get there).
Believe it or not, one way of making a little money is through Exhibition. Having Lin take her top off or selling Android's milk will get you $10 each. There's also selling girls' pinups, but that requires a bit of Affection and Exhibition plus buying some of the outfits. Of course, there's also an event where you get $10k, so that helps. The best advice I can give is to try to spread out your expenses as much as possible. One reason to try to spread out the upgrades is to try to save from spending too much too fast and finding yourself broke for awhile.
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