The clear is much easier to cut and buff before it hardens so waiting till it's cured is just going to be harder work.As for how long after sanding,I've alway's buffed right after. The sanding is to remove the 'peel and nib's so a day or 2 shouldn't matter much.
You can get a cheap buffer at Harbor for less money that will do a good job.
The larger pad will mean less work and IMO a flatter looking finish as opposed to a 6" pad on an orbital DA or such.
I suppose a regular orbital would work OK but I have no experience on using one for this.
Compound would be
3M Perfect-It III Regular cut for the inital with a wool or flat foam pad.
3M Swirll remover with a black waffel pad.
3M Finishing Glaze by hand.