I know that there is a performance park that came with Showtime, but I just want to add a stage to my existing towns that I have downloaded. Do I just add a platform to the park? Does it have to be a certain size? Do I need to add an object to it?
I bet if you switched from "Big Park" to "Park Venue" or whatever the parks that have proprietors have are called -- I saw it this afternoon when I was looking at the new lot names but I can't remember what it was and it doesn't seem to be in the wiki yet. Anyway, if you go to Edit town, and change the park to something that has park in the name and is near the coffee house and other showtime venues, you'd find out if you had a sim buy the lot. When you buy the lot, you have the option to click on "Real Estate" and it will tell you what objects you need to get the venue working.
I wish I actually knew what you needed, but I usually buy a lot (with cheats sometimes if I'm not playing a challenge) and then see what the game tells me the lot needs.
To build a stage like they have in Performance Park, build a...I believe it's 8x7 foundation (or platform). Under the right-most Debug tab in the buy menu with Buydebug on, you'll see a flat object labeled as a stage. When you place it it should be orange checkerboard or some stupid color like that, but you can recolor it in CAST. If you want your stage to look more professional, down towards the bottom of that list you'll see the lighting/awning rig for the park stages, a sort of stage scaffolding system that fits around the foundation with room on the side for you to add stairs. The same also exists for the other venues (or at least Big Shows, I don't recall the rest). Outside of the buydebug tabs, you can also add stage decor as the venue's default stage layout.
I've yet to determine whether it's necessary but the Performance Park venue makes use of the little squares under debug that tell the audience where to stand. Specifically, EA used the one labeled for table seating (and then just didn't place any tables on them). Try it without first, I've had that item cause some resets a few times.
Proprietors should spawn on their own.
Other than that...Live Venues (like the included Karaoke bar) are pretty obvious builds, although I'd use a platform for the stage instead of a foundation. The private venues I haven't tried to build but I'd imagine it's similar. And the big venues I think would be complicated enough to mess around with that it might be best to just use the prebuilt lots. Big Venues have their own audiences and crap like that to try to make work.
Snickerson: a Random Legacy Challenge. There are zebras involved. Zebras.