I don't have experience with either of the two cars you suggested (they are both very popular though), however, with regards to your engine question; you will need to put your own engine in it (and probably all the electronics, etc). As for the size, today's .21 engines probably have more power than you'll ever need in most race situations. In addition, .28 size engines are not sanctioned in most organized race meetings / competitions.

It depends on what you want to do with the car. Race or Bash? Bashing.... a .28 is fine, but then again, i personally wouldn't shell out that kind of money on the cars you've mentioned just to go bashing with. There's plenty of other very good (and less expensive) bashing buggies out there.

Don't forget a couple drops of after-run oil after each time out with the car.

Welcome back to the addiction.