Dog gives warnings when handled (snaps air or puts mouth over handlers hand) Behaviour

Hello everyone,

I recently adopted a 2 year old malamute-husky mix.

He doesn't like certain handling (some grooming, having his paws touched, too much petting), and will let me know when he's had enough by either snapping the air next to my hand, or sometimes putting his mouth over my hand, but not biting down.
I've mostly figured out what he doesn't like, and can avoid bothering him in these ways, but sometimes he can be choosy. For example, he always lets me pick up his front paw to put it through his harness, but last night he was really tired, and not in the mood I guess, so he got mouthy (but not in a playful way).
He will often roll over and paw at someone for a belly rub, and then after a minute, he's had enough, and he'll snap near their hand to have them stop.

I can mostly manage his interactions to avoid these things, but I obviously don't want this to go unchecked and get worse.

Whenever these things happen, I just remain neutral. I don't want to discourage him from giving a warning, since it's better than the alternative.

Does anyone have any thoughts on this? We are going to see a dog trainer next week who can hopefully provide some guidance, but I'd still be interested to hear some different opinions.

@GsdSlave