Hi Andrew
Rules are such that there is always a class for every car on any tyre. If the sprinting bug bites, you will want to get the right tyres to put you in the lowest possible class, but this can become expensive when wheel/tyre combinations are not strightforward, tyres aren't available, and if rules change. I'm sure the intro to sprinting day will help with advice on all of that.
For a 1.6K, if you are 5 speed, you can probably complete in class 1. Popular tyre for class 1 is Yoko A539. But CR500s not allowed.
If its 6 speed and/or Supersport, you are probably in class 2 or 3.
For class 2, popular choice is Yoko AD08 (but difficult to find now, and needs 15" rims), or Yoko A539. CR500s not allowed. (And new ADO8"R" not allowed!)
For class 3, CR500 is allowed. Others tend to use soft compound Avon ZZR or Kumho Ecsta (and if K series on those tyres, also tend to have dry sumps to cope with the impact of high grip on oil surge). Yoko 48, Toyo 888 also allowed.
Best advice is to use what you have and know for first few events, and not spend £££ upfront other than mandatory safety equipment (suit/boots/lid/gloves/rollover bar).
AB
[Just don't ask whether ZZRs are better then Kumhos as you will fall asleep while the "experts" witter on for hours]