T-prop doesn't always mean "rapid upgrade". You can refer to the guys at CommutAir on that one. Their upgrade time is equal to or more than some jet jobs. Go for the airline that will offer you the best QOL in your opinion and stick it out there...try to avoid switching regionals as this only hurts in the long term (read as avoid Mesa, GoJets, etc).

"Jumpseating" is something only pilots (and some other aviation folk like the FAA, Dispatchers, ATC, etc.) can do. One could fill an entire thread about it, but the basic jist of it is, it's a way for pilots to get around on almost any airline, regardless of whether you work for them or not. Non-rev is a completely different scenario. Most regionals will give you and your immediate family (mom, dad, wife, kids) non-rev benefits on whoever your flying for. So, if you're doing flying for Delta, everyone can fly standby on Delta.