There is nothing wrong with over building it to enjoy it later. BELIEVE ME I know all about over building. What I am trying to convey is that there is more to it than just rods and pistons. If he thinks he will want to up the power than he needs to go ahead and address that now but not just with the internal parts. There is no point buying 440cc injectors only to replace them later with 1000cc same with the turbo. A nice turbo sized for his current goal probably would not serve him best at significantly higher power levels. Same with a clutch, etc etc.

If he thinks he will want more than he should just set out to build to that point now, Rather than spending the money twice.