the IDP is I believe still valid when carried with your home foreign licence for 3 months, so would be okay for most tourists. Should you wish to stay in Thailand longer and drive it's then you need to get a Thai driving licence and of course have an appropriate visa.
In England I always wore Shoei helmets (and I'll be bringing across a J-Cruise to use in Thailand). Do any Thai lids meet international standards? Having only looked briefly at them they seem no better than my horse riding hat or my cycle helmet.
I noticed too that so many riders in Thailand seem not to attach them properly.
Thailand Digital Arrivals Card. It's similar to the paper slip you were previously handed on the aeroplane just before landing. Now though you fill it in online up to 3 days prior to arrival.