Hey Eater!
Welcome the community and I will be happy to help you out.
Scottrade wants you to deposit $500 minimum in, but that is it. So you can have all $500 invested in a stock and have $0 in cash and you are still ok. The reason they ask for a minimum deposit to trade is make sure you are serious as a client. Hope that answers that.
Secondly, when placing that order what you are going to do is first take the position as in buy it with the limit order, then once you actually have the position you fill out a new order for the stop loss. Basically, they are two separate orders. The reason you can't place both at the same time is because you can't technically sell something you don't own yet.
Hope that helps, look forward to seeing you around more often!
