For (1), test profusely beforehand, and apply your algos in paper trades first (demo APIs without real market execution). And of course, hedge your bets, don't put all your cash on one algo/instrument in one go, and do at least some DD.

For (2), there are zero-fee brokers (e.g. those mentioned by downvoteme1 earlier) that you can use, so you don't have to keep feeding the broker.