i've never used sealant before. Good job?
yeah the sealent, seals the polish, so it gives it a longer lasting shine - i know it sounds salesman like, but its true, then you just top your wax up every 8 weeks or so, rather than going through polishing it all again.
I would recoment every 6 months redo it all again - polish seal etc.
If you put 2-3 coats of polish, and 2 coats of sealent and top up with wax every 6-8 weeks, it will last you 6 months