county tax office will have a place to register your business, get a dba certificate, and check if your business name is already taken. ($10) usually.
A business plan is not necessary. Well, a plan is always necessary I guess, but a formal business plan is generally for others, not for yourself. This sort of thing should not require any real capital, much less anyone else's capital, much less a bank's. You're first post is perfectly fine as a business plan.
keeping every little receipt, forecasting earnings, and all that fun stuff isn't necessary.
The irs ruled that CC statements can replace receipts, ask your cc company for a second card tied to your original line of credit, no need to open up a new one, just a great way to seperate your statement and keep track of business only expenses. Also, anything under $75 written proof is not necessary. The irs can disallow it, but you can't get in trouble for it, and if the irs is looking that hard at your little computer firm running out of your dorm you have bigger problems then a dissallowed $3.99 pack of bic pens.
business insurance and contracts and all that fun stuff designed to protect you can get expensive. I would go as far as a small disclaimer at the bottom of an estimate that they sign, but I certainly wouldn't pay for insurance or to incorporate.
p.s. take your dba certificate to the bank and open a dba account under your business name, most banks have free small checking accounts that beat the shit out of free personal accounts. Don't bother with taking cc.
Don't turn what can be a fun and rewarding experience into a headache.