1) As a Captain, yes you will be able to put some money away assuming you don't go out to dinner every night. As a First Officer, doubtful you'll put much if anything away if you have kids (single guys could probably do it depending on their "social" activities within DXB).
2) Poor availability for North American education; slightly better for British education. The expansion explosion within Dubai has resulted in many of the "softer" infrastructure items being left behind (schools, hospitals, public transport, roads, etc).
EK makes NO effort in this regard. They pay you a fixed allowance (which will probably not cover the full cost of education depending on the school you choose and the ages of your children) but you are on your own finding a place for your kids to go to school.
3) I doubt the time to command will change (other than the odd "bubble" that occasionally creeps into the system). I would guess that at least 80% of the new hires within the past 1 1/2 years are former Captains that meet the EK Accelerated Upgrade requirements. Also many of the F/O's that were "left behind" when the rug was pulled out from under them when the rules changed are now coming up to the required hours. As such, I would be very surprised if the average time to command for those joining now would be less than 3 years. If you come and count on 3 years you won't be disappointed but I wouldn't count on any earlier (but like everything at EK, that could change overnight).