And if you mess up and promise something that falls through, it is a good idea to 1) admit that grownups make mistakes, 2) say you are sorry, 3) come up with a way to make amends, and 4) expect that none of that will make one whit of difference to the fit he’ll have (but it will make a difference later).
Offer choices from limited options that you can get behind: “Would you like to color, or watch a video now?” Not “Would you like to go to a movie (don’t know what is playing when), or color, read a book, or bake some cookies (don’t know if I have all the ingredients), etc.” They like power. If they can get you to let them manage more of their day (within pretty set parameters - don’t tell them you are still really in charge), they often love it.
Spend as much time at his physical level as absolutely possible. Kids this age (and most ages, really), love grownups who will get down on the floor, who squat down to eye level to talk to them, and who basically stay eye-to-eye. If you can’t get down for something, lift him up - a chair turned backwards to the counter so he can stand and watch you do the dishes (or help) is great. If you decide to do any things like cooking together, stick to simple tasks like pouring the measured items together, or even more fun, tasting all the ingredients before the get put in!
He’s more likely to have accidents (potty-wise) if he’s absorbed in an activity. So remember to ask about potty breaks.
Sounds like a great time. I happen to like the 3’s, but they can be volatile…