I run at those tracks in the Yamaha Senior class and follow the Junior Class very closely. As far as what kart to get I would recommend an Arrow X1E. That is the chassis that I currently use and have had excellent success with it. I also have had great luck with my other chassis of an Arrow X1-28. For parts for the Arrow they are available through Kustom Kart shop who shows up to the track and also can get you the chassis (it is where I get mine from). I also would recommend the Arrow X1E because it was one of the fastest chassis at the last WKA national at GoPro Motorplex with Gresham Wagner.
As far as what the leaders run you are running against 2 very good national people of Brandon Jarsocrack and Austin McCusker (Sorry guys if I spelled your name wrong) both on the Hasse chassis. There are also a lot of top karts in the field but I do not know what models for either the Hasse or the Top Kart.