is there a good hight to have your buggy of the ground at the mo it is 5 cm off the ground what should it be
Generally you'll want either an even ride height (front & rear) or a bit of forward rake (rear higher than front). On my RC8 I'm running 29mm front, 30mm rear... but I'm also running on a rough/bumpy track and not hardpacked clay or blue groove. Your droop settings and suspension travel also important here.
A lot of your setup depends on the type of track you'll be running on and the kind of buggy you're running. We can give better advice if you can provide some more info.
In addition to the suggestions above, I'd add a couple other things:
Know your run time. During practice prior to the race, once you've got everything warmed up and running smoothly, fill the tank, fire up a stopwatch, and run some consistent laps at 3/4 your race speed until you run out of gas. This let's you know when and how often you'll need to pit during the longer mains. If you're on a 40second track (ave. lap time) and your runtime is 9 minutes, you know you'll need to pit at around 7.5 minutes. Leave yourself a buffer.
Make sure you have fully charged batteries, glow plug, starter box. In the pit you should also have a philips to fine tune needles, an extra glow plug, temp gauge/stopwatch, extra fuel.
Work out ahead of time how you & your pit guy will call you in for fuel. Is he tracking your time or are you? Practice refuel pit stops.