hi,
many online casinos dont let you play blackjack with your bonus money, but you can find a list of the ones that do here
www.bewisebets.co.uk/casino
in terms of depositing i usually use my debit card as it is often the fastest method of depositing or withdrawing. Neteller is good, although im not sure about charges. These are more than likely offset by the extra bonus cash that they offer you for using neteller (usually in the region of about 15%) hope this helps.