I would highly suggest renting an
ECV from an offsite company. I'm assuming you'll be pushing the 2 year old in a stroller where possible and there's no way your husband is going to be able to get around the parks walking with the boot, on crutches, or using a manual wheelchair on his own. Even if there was a way to cut down the amount walked/waiting for attraction lines, the majority of walking and standing is between attractions, getting to/from parking lots, walking around your resort, etc. The offsite rental places will deliver/pick-up from your resort (or most places in the Orlando area, it seems, including hotels, condos, etc.). Renting offsite means that he'll have the ECV if needed at the resort and that he'll know he has access (the parks can run out of ECVs fairly early in the day). If you don't want to deal with the buses, you can rent a travel
scooter that can break down and be put in the back of a car. Please note that when the ECV is on (even if stationary), it's not safe for the 2 y/o to be in his lap. It's not allowed by the rental agreements, but it's also just plain not safe because it's too easy for a kid to hit the controls by accident. If you do have him practice in a grocery store or box store first, know that their scooters are far harder to maneuver (and slower) than the scooters you rent from offsite companies for WDW.
ECVs generally go through the same queue as everyone else. Sometimes you'll be diverted partway through or go through another entrance, but that doesn't mean you're getting on faster. Sometimes it will be faster, sometimes it will be slower, and sometimes it will be the exact same amount of time. He can park the ECV (with stroller parking is usually a safe spot) and walk the queues, but for the Safari and if he tries Soarin' (which is the one ride where a WDW employee might think he wouldn't be safe with the boot, but I'm not sure) he'll want to take the ECV through the queues. Those two queues are 1/4 mile one way, there's no way to cut down that distance (the fastpass line is just as long), and you have to walk the 1/4 mile out again at the end as well.
Since he can transfer, he'll be able to go on the majority of rides. Peter Pan cannot be slowed or stopped for boarding, but if he can get on in the allotted amount of time, he can ride it. The Tomorrowland Transit Authority also cannot have it's moving walkway stopped or slowed (and has no wheelchair accessible entrance so he'd have to be able to balance on the walkway). Every other ride can be stopped or slowed.
I'd definitely suggest planning in breaks. Pain and healing from an injury do reduce your energy. You do not need to fit in everything into this trip. WDW will be there and quite honestly chances are your 2 y/o won't necessarily remember much. He's certainly not going to notice if you don't do everything because you all need breaks. Plus taking breaks for naps and stuff will also help keep everyone happy.
If he is resistant to the idea of an ECV, ask him if he can walk 6 miles a day, multiple days in a row. The average WDW guest walks at least that much and, as I said, the majority of that is not in queues. He can have a great trip. WDW is one of the best places to go on a vacation with mobility issues. As a family, you just need to re-adjust some of your expectations. And keep an eye on him. He probably will try to tough it out past his limits, but everyone will have more fun if you can manage to reduce that (especially if you can do it without making it sound like you're taking a break because of him; suggesting a snack in an air conditioned restaurant or naptime for the kid are both things that might help.)