1. jetting is very personal. Answers to jetting are like eyebrows (filters prevent using alternate, more appropriate term
). First step is to see what's in there now. Then maybe step down a little on the pilot and needle. Also check the float height. The horizontal mold line on the plastic floats should be parallel with the gasket surface of the carb body when the little arm "just" contacts the needle plunger (not allowing the little spring loaded tip to compress)
2. Regarding plugs, I make it a habit to run 1 heat range hotter (NGK "7" rather than the stock "8") in every 2 stroke I've had in recent years. There is absolutely no harm in this unless your planning to run at Bonneville as there is lots of safety margin there. The hotter plug means the tip runs hotter and is more adept at cleaning itself at the higher temps.
3. Steel spigot bits are available from LTR Racing (a sponsor of this site, so links are readily available). Les has shipped to the UK many times, so that's not an issue.
You shouldn't have to think about fouling when things are set up correctly.