Welcome to the dark side of fishkeeping! lol
Okay, on to the thread. For starters, a clown in a 20long would work so long as you kept the 20L open, not to much LR. Now, I recently bought 20lbs of Live Rock. Cost me $200 to do so. So... yea, salt water is expensive. I would (if I were you) save up for however long it takes to reach $1000, then buy the best possible equipment and a 30tall (aprox 29 gal). The 30tall would be plenty to house a clown, and I would use around 40lbs Live Rock (it's what I have right now). You stocking is fine for a FOWLR, but dump the bicolor if you go reef. As for the sump, I'm going to be using a 20L as my sump soon, and sumps are always a good idea with salt water. Lighting.... ouch, it's gonna hurt when you find out the price. I was looking, and the average cost was between $80 and $200 for lighting.... so yea.
When I first started all I bought was sand, LR, salt mix, fish, a filter, a heater, and a powerhead.. Cost me almost $400 back then. Now I added $200 to that for my 20lbs of LR I'm adding to the system, and probably another $50 for new stock (lost all but one for various, mostly unknown, reasons). The sump will add another $300 or so, and lighting for a tall tank like mine... $300 more. Totaled, that $1250 as my bet for my future set up... You will not get far with $100... Yep, I'm a party pooper who just killed that dream, aren't I? lol, sorries.
So, once you have the money, you can start the set up. Get 2 decent powerheads, decent lighting, no filter needed, heater, 20-30lbs of Live Rock for a 20L, 30-40lbs of Live Rock for a 30T. Sand substrate. Start without corals or fish, let the tank cycle (about a month ta two months time, I think). Then add your clean up crew (hermits, snails) and feed every few days. Around a week after that, add the smallest of your fish, then a week later the next few fish. never more then 3 fish at once, to help prevent a mini-cycle.
Now, I may be missing something, but did you say you wanted a 10gal nanotank? At best, stocking would be a pair of firefish and *maybe* corals if you get a good light. For that, maybe a filter. 2 smaller powerheads. Heater. Total cost around $300 or so.
I would not do the 10gal nanotank, they are hard to keep stable. Bigger is generally better, so go as big as you have space and money for. I think the 29gal would be the optimal option, if you can afford it and care for it properly. Save up $$$, read up on info, and take your time. Oh, and don't do what I did and try to rush it, that will ALWAYS end in disaster...
Good Luck, and hope I didn't crush the dream by pointing out the probably price
~Siv
