Double deadhead refers to a deadhead at the front and back end of a trip. Every fleet has them, seniority to hold them varies, but isn't out of the question to get them as soon as you get off reserve. Not sure you can quantify exactly what seniority it would take in any given seat to hold such lines.
Yes you can use the bank money to fly from Hometown to the designated city instead of Memphis to the designated city. Onus is on you to get there on time in the event your deadhead flight gets jacked up.
Commuting on FedEx is probably as easy (relatively speaking) as it gets short of home basing.