What would be a good number of chin ups to do, a a future goal ? (with the palms facing in)?

20, good enough, but the thing is, never stop. You will be a righteous old fart that can do 20 chin ups.

Whatever you think. Talk to a personal trainer if you want to know. We aren't personal trainers.

There is really no limit. In or out doesn't change the difficult a lot.  At some point you will want to start wearing a weight belt to keep the reps in the 8 to 12 range.

I think it depends on your body shape.  When I was in high school, I weighed about 200 pounds and was 6-2.  I think my max was like ten or eleven.  But some small skinny guys could do almost double that.   I once met a Japanese guy who did Kendo in university and he could do five chin ups with one arm.

for me, One lol

start with one.  make sure you have good form.  you're actually pulling.  not lunging up there or any other motion.  practice hanging there flexed.  do it for 30 seconds at a time.  then try to do 2 or 3.  then 5.  then 10.  etc.