I recently set up my first reef tank after keeping freshwater tanks all my life. I am 21 and a senior in college (just couldn't wait till after graduation to start) so I definitely have some limiting factors as far as time and finances. I set up a 55 gal which I personally think is a great compromise for a first tank. It is big enough to keep good water quality but not as expensive as a 90+ gallon tank. Overall you need to research and decide what kind of tank best suits your purpose. You mention a reef tank with corals so you need to take live rock and lighting into consideration. I spent $200 on live rock and I could use about $100 worth more. A 90 gall would need twice as much, so you could easily spend $600 just on that. A 55 is also a good choice for your lighting needs. It is not too deep so you wont need to spend tons of cash on metal halides. You can choose 4-40watt flourescents, like i did, or 2 VHO's or HO's. This should be plenty for your easier corals in a 55 gallon, but with a deeper tank you'll need more light, which is more money. Also, so far you only have 3 relatively small fish picked out, which probably wouldnt even dent the biological filtration capabilities of a 55 gallon with live rock and sand. I have a royal gramma, pygmy angel, and 2 neon gobies in my tank right now and have a hard enough time trying to find them when theyre hiding. In a 90 gallon I'd never see them! From what you have told us, it seems like you don't need the extra size of a 90 gallon tank. However, if money is not a concern and you plan on getting more/bigger fish in the future, go for the 90 gallon. Just know that it's not necessary. Hope this helps, and have fun with it. I wish I got to have a reef tank when I was your age!
p.s. I don't have any personal experience with starfish, but usually they are a concern when keeping a reef. They can accidentally knock over your rocks, damage corals, and eat certain inverts. So make sure you ask a pro about it before buying. You can probably call someone at liveaquaria and ask. Brittle stars are pretty useful and safe however. Also check out etropicals.com, they are a sister store to liveaquaria and have a lot of the same fish for much cheaper prices. an example is the royal gramma, i think its $12 at LA, $8 at ETrop.