I'm pretty sure that you have it mostly right, but always triple check the following link and speak to the series organiser before entering (they will be happy to help):
https://www.msauk.org/assets/325336s...ragracings.pdf
Other things:
Tyres. Depending on the series, you may be allowed 1B tyres.
You need gloves in addition to helmet and overalls (check ebay for overalls!).
I would not compete in an MX5 without adequate rollover protection.
Supercharged MX5 should be excellent fun! Which locations are you thinking of?