1. Is buying, is baking, is decorating (pres. cont. with the future meaning)
2. Are you doing (pres. cont. with the future meaning) or are you going to do (the structure for planning); i'll stay (future simple).
3. It's going to rain.
4. You will fall (future simple)
5. Will be (future simple); we are having (pres. cont. with the future meaning) оr we are going to have; are you going to invite, have you already invited (present perfect).
6. Does this bus leave (present simple for train, bus and other vehicles); i will go (future simple)
7. Is he going to be; he's leaving (pres. cont. with the future meaning) or he is going to leave.
8. We will be late.
9. Gives (present simple for events), he's going to fly.