I do. In fact when I open a live account I will open a demo account that mirrors the live account (i.e. same leverage, balance, margin) exactly. I will even go as far as having them running at the same time and opening the same trades.
I'd suggest that you choose your broker carefully. Many have a dealing desk (that shows higher price over what is being traded real time on the IB), and pip spreads can differ quite widely between brokers (in addition to there being other hidden costs of trading live).
MT4 accounts can be retained as demo's or for tracking other entities (oil, metals, indices etc) but when you get to live trading, make sure you have tested and compared a variety of brokers. Start with looking at Oanda's comparative broker spread table here -http://fxtrade.oanda.com/forex_trading/why_trade_with_oanda/spreads/compare_broker_spreads.shtml
I'd suggest that you choose your broker carefully....
spreads arent the only thing to consider: the main difference between brokers is price feeds. yes, spreads play a part in this, but they are only a piece of the pie. some brokers get their feeds from a third party and usually have fixed spreads and such. these are usually ECNs and bucket shops. others actually provide the prices themselves. because of this, spreads AND prices will be very different. also, just looking at ECNs, some might take their feeds from one bank, others might get them from multiple banks. this also accounts for a difference in price.
the best thing to do would be to find two brokers that either have the same price feeds, or feeds that are very close. if your system is very price specific, or based on moving averages or whatever, this will be very important.
Yes, the price differential ex the dealing desk factor is important for charting purposes, especially for candles. Several other things to look for in comparing brokers -
1. The swap factor.
2. Use only fully licensed and registered fx brokerages (so that you have come-back if there is a problem with your account or trades.)
3. Funds transfer time & procedure (both in and out, and reliability of this).
4. Capacity to trade in own currency.
5. Precise and immediate execution of stops, sans lag time.
6. Platform performance during busy periods.
7. Spreads during news time. These often widen considerably, all brokers differ.