I don't and haven't owned a FedEx route, but I did work for one of their competitors and managed a small parcel operation. There are a few things you should consider if you're looking into this...
Drivers will be your biggest obstacle/headache (shocking, I know). The operation I ran was a true IC model with several IC's having 2-3 trucks running routes, and there wasn't a day that went by where there wasn't an issue with a driver showing up an hour late (if he even came at all) or deciding to come to work with an attitude. I employed 2 hourly "swing" drivers who would often be sent out to ensure we met delivery expectations from a driver being late or no showing. Due to the IC model, that was a cost I had to eat. The IC didn't like me "taking their money," but they did understand the commitment we had to on-time percentage to our customers.
If the Texans or Cowboys play Sunday/Monday Night Football, plan on having late drivers and no shows the next morning (include Sunday/Monday holidays as well). Since they'll be your employees, you can handle it however you feel is best. I dealt with the IC's, so I had no say in how they handled it but did have some indirect influence.
Like everybody else, drivers have a comfort zone and asking them to get out of it would make you think you're asking them to give up their first born. Lets say you have a route that covers the Energy Corridor and Katy, and the dividing line is Fry Rd (done by zips, but whatever). One day the EC guy has more than he can handle while the Katy guy could use a few more stops/deliveries, so you ask him to take a couple that take him out to Barker Cypress. He'll fight it tooth and nail about how he doesn't know the area and can't do it. He'll probably even threaten to quit. Having the extra deliveries is nothing more than a mental thing that will linger with him all day and could potentially impact how well he runs his route
I'm not saying all drivers are bad, but they're a special breed. It takes a certain type of person to be successful at it, and you'll probably turn over several drivers before you find a good one. When you have a good one, you do what you can to keep them as they'll make your life a lot easier. It's hard work with long hours, especially from mid-November through New Year's, but there's money to be made.
Technology is something else you need to be aware of. I'm not sure if FedEx provides the scanners or if it's your responsibility to buy them. If it is your responsibility, I'd suggest buying a couple of extra. They will break and there will be software issues, so having some extra to send out while you send the other in to be repaired will be needed. Not sure of the exact scanner type FedEx uses/requires, but ours were around $1500 per scanner and included an extended warranty IIRC (2-4 week turnaround on repairs). You'll find that some drivers catch on to technology with ease, and you'll not have any issues with them, but you'll also find drivers that look at a scanner and will make you think it's speaking Chinese to them. You'd think that would be the older drivers more so, but it really does apply to all ages. It's quite fascinating in today's world to see somebody who can't follow a few basic functions to scan an item out for delivery, delivered, or attempted. The real kick in the nuts is when a driver kicks ass on the delivery part but is a technological midget. We tracked scan compliance and held the IC's accountable for it, and I'm positive FedEx does as well.
Ok...well, this went a bit longer than I intended. I'm not saying this will apply to you or that this covers everything, but this is some of what immediately popped into my mind from managing a similar operation at one of their competitors.