for the kart you bought, your better suited for TAG, HPV (think its called something diff now)
I personally wouldnt go chonda i would do LO206 but the 50 mm axel might not give you the flex you will need. but thats my opinion. I know David has been karting a lot longer then me.
Also I you dont want to spend a gazillion on mychron, and you have andriod phone, check out an app called track master. pretty powerfull data loger for a fraction of the cost.
When i get a new kart i set everything to neutral until i get consistent laps, then one or two adjust for 5 laps and see if the times got better.