I would give kartsport a call and either talk to Brandon or Eric Jones. I would recommend you first just get the margay you have with the methanol engine and run that for a few practice days if your son is able to fit in the kart. Try to get with someone that can at least go over the kart and have it assembled properly with the correct size seat etc. If the margay kart is not the sportsman/cadet model then he will have difficulty reaching the pedals without major modification. You will also want to be CERTAIN their is a very small restrictor in the motor if their is not one already installed. I would also not give the kart more than half throttle even with the plate for his first session and make sure he is on track by himself the first time. Safety should be the main concern to start with. Also need to make sure the throttle returns easily and the brakes work well. At 7 years old it actually would be more appropriate to try a “kid kart” which is a 50cc comer engine scaled down significantly for young/small drivers.
Don’t be scared by what some spend on budgets at national events. That is not exactly the norm and at the local level many spend less than a few thousand for the entire year once they have their equipment. Post any questions or message me and I will be happy to help. The LO206 engine is the way to go for both beginning drivers and someone on a budget. Basically a brand new race ready engine package for 750 that you can run all season with little to no maintenance. Just change oil once a day and keep pump gas filled up. It’s the fastest growing class at Mooresville from what I understand.