1. I am not familiar with any airline that strictly forbids commuting, but some are more friendly about it than others. Some airlines have commuter clauses built into their contracts that certainly make it easier. But I'm not familiar with any airline that won't let you.
2. You can most certainly change bases after you're hired, but you can only go to a place that your seniority can "hold".
3. The ability to commute has little to do with distance. (Except for if it's close enough you can drive it if you really need to.) It has more to do with how many flights a day, what airlines are they on, is your airline CASS, is the airline you're trying to get on CASS... is the airline you're trying to get on your own..... Is it a popular route.... Are there lots of people trying to do the same commute...... etc..... The number of things that can mess with a commute are endless. I did Chicago to St. Louis when I was at Trans States, and you would think that would be an easy one. AA sent several MD-80's and 757's throughout the day. United sent a couple of 737's. Trans States has at least 3 or 4 145's a day. And finally Southwest had about 8 daily departures. But it was a *****, Trans States wasn't CASS, so the Southwest cockpit jumpseat wasn't available. Lots of Eagle pilots commute back and forth because they were ex TWA. So the American flights were never realiable. United only sent a couple 737's and they filled them up fast. Most of the United flights were on GoJet and as a Trans States pilot I wouldn't have been caught dead on one of those. And finally the Trans States flight were always at the very beginning of the day or the very end, so it was hard to risk taking those because if you missed it, you probably missed your assignment. I'm now with SkyWest, living in Chicago in domicile. I can't stress enough how much better it is. I don't lose out on days off to commuting, and I remove the stress of constantly being worried about making flights. Commute if you must, but avoid it any way possible if you can.