Is anyone currently using automated trading with Fidelity successfully? If so can you please share what kind of issues you have or are running into? Any hints, tips, or warnings?

I'm getting ready to start once all my code is converted from daily to minute so that trade changes can be handled during the day.

Some questions I'm curious about are (some are discussed in the documentation but I'd like to hear from people trading specifically with Fidelity and automated systems):

1) How are you limiting the number of positions that are opened based on current open positions, margin requirements and orders that meet entry criteria?

2) If your strategies use things like sell on the close are you converting your daily charts to minute charts and placing market orders? What time are you doing that: 3:50? 3:55? 3:58?

3) How are you cancelling open orders? If placing an order to replace an open order will it cancel automatically (it doesn't when placing an order manually)? Or are you only placing orders when it's time to sell as market or limit orders?

For example, if you have a time based exit for the end of the day but are willing to accept a limit before that, do you follow minute to minute and place a market order when the limit is reached and sell at 3:58 if the limit is never reached? Or do you place a limit order, cancel it before the close and then place a market order?

Thanks in advance.