1. You don't need a SecondLife account. Fill in 'none', if you just want to trade.
2. They are balanced on your account. You have to withdraw the BTC. Withdrawals will be manually checked by VirWoX
3. btw. you cannot buy bitcents. Just 1 BTC or 100 BTC or sth

Please use my Afflink (in my signature), if this was helpful