Hi, and welcome to reefs.org. I hope I'm not steppin' in on any toes here, but I'd advise you to put your inverts in first. They tend to offer a much lower bioload, and animals like the blood shrimp tend to be a wee bit shy.
Also, honestly, I worry about the percs growing rapidly, outgrowth in a system that size is a real concern. What about something more along the lines of clown or neon gobies, with say.. a Centropyge argi? (That little fish will likely not "let" you introduce much else besides small gobies.) I think a Royal Gramma might be pugnacious (and slow-growing) enough to stand its ground with C. argi (this is also one of the toughest little angels you can find).
At this point, I think that if you want to add something like a soft coral, you'd be better off deciding what you want first (green star polyps and some mushies can be nice), and go from there. If your heart is set on those percs, then I suggest you either be sure you can sell them back to the shop (for credit if they're fair), or you'll have a bigger system to move them to when the time arrives. Remember, if you're good at this stuff, the time will be sooner rather than later.