We don't have a plan yet? Can you help us decide? I saw a predator 420cc engine at Harbor Freight. It's cheap and I'd like to use as that to power the kart.
That's an industrial engine. I thought you wanted bike power?
You need to come to some decisions before proceeding. What type of kart are you after? On-road/race? Off-road/fun? Mini Buggy/Buggy? Suspension?
Is anyone in your group capable of welding and fabrication?
How's the budget looking?
Depending on these factors (and more) you may decide to buy a kart and fix/modify it, or scratchbuild the whole affair.
Welcome to the forum!