It sounds to me like you won't actually need that much to start off. My startup capital, excluding the actual merchandise themselves, couldn't have been more than a hundred dollars.

That being said, you have to be realistic. It sounds to me that you are doing something similar to cafepress - basically getting a bunch of artists to draw and produce a specific merchandise (for now), paying them a percentage while you take the rest, etc. That kind of business won't net you much money unless you expand, and since your profit margins seem low, it may work out to be a poor per-hour rate for the work that you're doing (contacting artists, updating site, going to printer's, buying supplies, etc). I won't continue to speculate for now - shall be interested in seeing your ideas later!

How much I made? Initially, before anime stores became prominent in USA (that's where most of my customers are), I could make quite a nice margin. But now with the competition, I'm just not cutting it anymore. Just as well that I'm shifting to a niche market. Basically, there isn't as much to be made as before. But something original still enjoy a certain amount of popularity since:
1) supply is usually limited, and
2) supply, if available, is rarely shipped outside of the country of origin.

Just something to think about while you write up the stuff :D Not going to spill all my money-making beans here now, am I?

I'd just like to add, though, that at the start you probably can't afford to pay for IP to the artists, so you may want to secure a few artists on a percentage rate at the start, re-negotiable after XX amount of artworks. Remember always to protect yourself - include a clear clause saying that if negotiations fail in R2, you still retain the right to reproduce the works prior to R2 of negotiations at the same percentage rate.

And so on and so forth.

See? I do listen during my Technopreneurship lectures!