sixonesix posted some great info. i completly agree with only making a small amount of shirts to start off with. you might think a design is great and not have that many sales, and a design you don't think is great gets all the sales.
as for start up costs, the more money you have- the better! i'm planning to start my own business, seperate from my and my friends already established site, with no lump sum of money. just $20 here or there.
for website hosting i'd check out this thread http://www.craftster.org/forum/index.php?topic=15995.0
there's lots of reading, but it's good to get an idea of good and bad experiences.
i wholesale with american apparel. all you need is a licensed business and tax id. (it might be different in the states) the price is good, but the quality isn't that great. many of my own personal items have ripped seams and random holes after one or two wears. i would still consign with them, but thouroughly check the items. many people love the made in america, sweatshop free factor.
i do basic silkscreening in my house, but i can't do anything complex. i don't have the room or money for equipment that i had in school. what i'm looking into right now is going with a company that supplies the shirts (or other items) and does heat press or silkscreening for you.
so far one of my favourites is brokenarrowwear.com
. the customer support has been great so far, but i have just asked them questions, not placed an order yet. they will do smaller minimum orders, but the price per shirt will be higher, which means you'll make a smaller profit. but that's how businesses usually start out.
the fact that you already have a cafepress site and customers is great for you, so you won't be starting out as an unknown business.
p.s. if you go the route of having someone else print your shirts, and you like what you get, can you let me know??? i'm still planning to shop around a little.