what is the hesitation here to get your son a PR? State your true intention here? Are you worried that he will have do NS?

We are PR's..son recently born. I havent yet registered him. If I register him on a long term social visit pass, how long is it valid for? 5 years? any particular disadvantages to it?
I understand when he is 5 plus, if he starts school in singapore, he needs to get a student pass...will he be eligible to go to local school? or only private / international school ? also how long is the student pass valid for? does it need to be renewed every year?
Any of you'll (both PR's) tried this route for your son? any major hassles or disadvantages?
Further, should our mind change after say 8 years and we wish to change him to PR status. Would there be any problems getting approval?