My 3-year-old son doesn't cross legs while sitting down. He keeps his legs like (<>). He moves his toes and keeps his two hands below the mouth (as if it is so chill) whenever he is doing any task or when getting excited he has this habit from 8 months. How to reduce it? Now in this month he learnt another habit of keeping fingers in mouth as if he was biting his nails.
Although some repetitive movements may be normal (what is normal, anyway?LOL), there are some that are generally considered socially unacceptable. Although I don't understand all of the movements you described, it sounds like you feel as if the repetitions come under the category of socially unacceptable. Perhaps he would benefit from some occupational therapy. Occupational therapists provide interventions to aid in more social participation, and treat repetitive behaviors. You haven't shared as to whether he is talking yet and if not, speech therapy might also be beneficial. An OT with some psychological background would probably be helpful, to determine if there are any behaviors that require other types of therapy. Good luck!