Commuting to/from Florida is notoriously difficult because so many pilots and flight attendants do it. Plus, you're traveling on mainline, so you are (usually) just above people using buddy passes. Add to that the fact that summer storms wreak havoc with the schedule, combined with seasonal issues (spring break), and you have a recipe for headaches. If your airline has a commuter clause (that is, if they don't punish you for commuting), it helps.

MCO is usually the hardest, but JB offers a lot of flights....that often have several of their own commuters. RSW will be the hardest because it will often be a 2-leg commute, and there isn't nearly as much direct service to the northeast.

The trick to Florida is getting across the state line in either direction, but as a junior regional pilot, expect to waste an awful lot of time commuting. If you can move closer to base, or to a city with a better commute, then do so.

As far as picking up flights into/out of domicile (some call them jetbridge trades), every airline is different about that. Some are very accommodating, and some are not. Most of the time, as long as it's legal per the FARs and the contract, they won't care. Keep in mind that a lot of pilots tend to trade with the same small cadre of other pilots, and it can be tough to break into that group, since those guys are often looking out for each other.

Generally speaking the trips will begin and end in domicile, but if a trip ends or starts with a DH, you can usually drop the DH (it opens up a seat the company can sell). If a pilot is looking to drop a leg or two or three to get home, you might be able to pick them up. Again, it has to be legal, and it can't compromise another assignment you have. I can't speak for the airlines you've asked about, but generally, Scheduling has some leeway to allow this sort of thing to happen because so many pilots commute.

Per diem is only paid when you are working, so when you are just sitting on reserve, you won't get paid per diem. Some airlines pay per diem for 1-day trips (out-and-backs), but many do not. Per diem on 1-days is taxable, whereas per diem on IRS-defined overnight trips is not. Per diem IS NOT part of your salary, and is not intended to give you "extra earnings;" it is simply a reimbursement for reasonable food expenses. If you are smart and aggressive, you can, however, pocket a lot of that money. If you don't take food, and eat when you're hungry, you won't see a lot extra money in your checking account. You can also get creative on your taxes and increase your per diem allowances, but that's a different topic for a different day.

Hope that helps...