I see where you're coming from, and I have a long-term project that is something like this and if you want to see its gallery state so far, I'm called Loanet there too. There's less of your theming ideas, but the build has room for some change.
You will always need practice. Visit the Maxis nightclubs and lounges in the game, they're not Builder level, but they're a gateway to understanding how to make a functional start. A bar, and lots of room to dance and socialise. It's a good idea to have at least one stage, and a DJ booth.
Here's a tip for these... shady clubs. The windows are always fully curtained or dark, if there are any windows at all. The outside should be well lit, but the social areas are more shaded, and your bouncer needs to be sheltered from the rain. Make sure colours pop out, rather than blaze indiscriminately. Some colours are more appropriate than others, and they all give different vibes - blue gives a techno vibe, red a passionate vibe, purple a potential raver's gig and pink for a teen club.
Don't feel restricted just to Lovestruck - it's appropriate but there's lots of other ways to utilise furniture from other sets. Build in the Night to make sure the colours pop, because that's when your customers will be coming. Don't be afraid to build down, as you don't really need windows. Maybe have your themed rooms in a 'VIP' area.
If you think most of what you're asking for can't fit into a 30x20 lot, you'd be wrong. My nightclub literally has a pool and social area on the roof. The bigger the area, the longer it takes Sims to get to places. Think about what you want customers to focus on - it's the bars and the dancing. You honestly don't need bathrooms for 8 people. If you're looking for realism, dressing rooms and a head office are more flexible.
