I can’t tell you about South West fleets- sorry, someone down there should be able to help.
A lot of people are still using metal masts and with a decent sail that fits it, you should have no real disadvantage on flat water and inland. They say the carbon rigs are better, lighter and more gust responsive, which is probably true but you still need to be good to get to the front.
I manage to get in front of the odd carbon rigged boat from time to time with a metal rig, although the good guys are always hard to beat.
My weight is 74kilos ish and I reckon I can sail alright in normal conditions although bigger guys are quicker in the breeze.
The red top mast should be OK- the colour isn’t the whole story though as far as bend is concerned.
Go for it! OKs are a lot of fun and the people that sail them are good company.
Bill