Want to double check if I sign a guy whos ineliable  at d3 he can play right away I should just gime  him more time in class?

he can play right away @ D3. yes, he will need lots of study hall to maintain his eligibility.

would it be best to float him a RS even though he can start right away?

when applying the redshirt, the main things I want:

high potential player - I want him around for awhile, at his best.
lower WE guys sometimes - need all the time they can get to get better
roster dynamic - do I need him this year? is this a rebuild and you will be bad this year anyway (more likely to RS)?
class structure - are my classes lined up they way I like? (that could be answered several ways - do you want a big class? even classes? an empty class?)

so, I'm not exactly sure how to answer your question but happy to give my 2 cents with more info. you can site mail me too if you'd like to keep it private since it sounds like you are actively in recruiting