A close friend had a son with the same issue. Had lots of drooling, very hard to understand, but still evidently a bright child. He just sounded like he was 1 1/2 when he was well over 3. They waited for his surgery because it was not a life threatening condition and he has recovered all his language skills. You will want to get it taken care of soon so that he has the chance to learn better speaking habits prior to kindergarten. Talk to your ped or family doctor first as you will probably need a confirmed diagnosis/referral for your insurance. Good luck and don't worry. I'm sure he'll be fine and catch up with everybody once the tongue issue is fixed.
As far as picky eating. It may be that certain foods are hard for him to chew. Let him be picky for now, you don't want him to choke. If he's under weight, try some of the Carnation breakfast drink powder in w/ his milk or such.
For hand weakness. I'm sure you can find a bunch of exercises to help build brain to hand development and hand strength. Some simple ones are - Punch a bunch of holes in a piece of cardboard and let him thread a piece of clothes line through it (or similar easy to grab string). Play games of tossing small toys from one hand to the other and back and forth with you. One important activity though is to let him work at an easel.(or tape paper to the wall and let him draw/ paint it) Those hand and arm movements are important for developing the brain connections he need for writing.
I hope this helps and again, don't worry.