Okay, I'm going to be a total dick for a moment. I've worked on a lot of movies and I can tell you the biggest mistake one can make is trying to do something beyond their scope/range/budget. When you say you don't have a lot of money and you want to shoot it at home, then you say you want to do a parade scene that is literally one of biggest things one could produce for a sequence, it makes me nervous.
if you're a miniature, green screen, and compositing whiz, or you really like the idea of learning to do that stuff and like a challenge, by all means you should do it. I think you should decide what you want feel when you have a finished product. Do you want something for yourself and friends to enjoy, something that shows the work you put in even if it isn't perfect? Or do you want something that could go viral and get you attention? Something in between?
i think you decide that first, then from there develop and idea that plays to that, and most importantly, can be done with what you have available. Again, ignore me if you want this to be your version of film school as you try things you've never done before. That's fully legit. But so is doing something smaller in scope if you worry your production assets are thin.
Theres a ton of single-room shorts and stories out there. Me, personally, I'd build one great set I know I could make work and not try to create a battle from thin air. A one room short can still be full of tension-- a rebel and an imperial are trapped in an escape Pod together, a Jedi is trapped in a cell and has to escape, two rebels have vital information to deliver but their ship is dead in space and life support is failing, smugglers hide with their cargo waiting for an imperial inspection team to pass, etc.
Want to expand the scope from there? Go outside and find a place in your area without people or structures-- forest, desert, rocky hills, whatever is by you-- now you have a sparsely populated planet.
Doesnone of your parents or friends or somebody work someplace like a factory, warehouse, sterile office, hospital? Any of those places could work if you can steal a couple shots to set up some scope-- long halls always feel like they are part of something.
I'd take stock of what you have available and what sort of product you want at the end and go from there.
Or, again, ignore me and have fun. I over think these things.