Have fun with your kids!
When I fly with mine I try to plan longer layovers than I would flying alone to give her more time to run around. MSP Terminal 1 is one of the best airports to fly through with kids IMO, there is a great play area by the little food court on the C concourse, perfect for wearing out the 2.5 year old.
I would recommend using something along with the standard seat belt for the 2.5 year old. My 2 year old's favorite airplane game used to be undo mommy's seatbelt, and is now undo my own seatbelt, not what you want if there is turbulence.

I would highly recommend wearing one kid if you can, or at least being prepared to wear the kid, so much easier. If you've got a double stroller you can put the older kid and carry-ons in it to get through the airport.
Word of caution about checking the carseat, Delta specifically states that if they damage it it's not their fault (some TA's make you sign the waiver most do not IME). Because of this it's better to gate check, less chance of damage that way.

The biggest thing is to plan, plan, plan. When I pack I go through everything in my diaper bag and carry-on and if I won't NEED it during the flight it goes in the checked bag (obvious exceptions are car keys, medications, etc), I want to be carrying as little as possible in addition to the kid. I plan out how we're gonna get through security, make sure anything that has to come out is on top and easily accessible. if your stroller folds up small enough that it will go through the x-ray scanner send it, huge time saver over having it swabbed down, obviously doesn't work if you've got a large stroller. The few times I've flown with kid and hubs I make him practice going through security so he knows what has to come out of the bag and off him. your 2.5 is probably mature enough that you could get him to help and he'd love having a job like take the Ziploc out of the big bag and put it in the bin. If you do wear the younger one only part of the time try to plan to wear him through security, most TSA have let me keep my daughter on my back going through security.