As you say, the welsh scene may indeed be small, but what about it? The irish scene is tiny but we still had two teams coming away with silver ware from various M5 divisions. Quality, not quantity
Small is not such as bad thing as it means that there is more control over certain aspects and it may mean organising events a lot easier because there are less things to worry about.
In terms of management / organising, my idea was for each country to put together their own governing body. The UKPSF would be the uk version, the IPPA (Irish paintball players association) and perhaps the welsh and socts could set up or organise their own.
The idea of these associations is that they can / should be able to put together a team or organise an event and fairly find the best in their country. A players body running it, means that there may be less influence by a profit making business and some decisions may be made by hidden agendas.
That said, companies will need to get involved i.e. we will need a place to have the events in each country and sponsors will have to get involved in order to help with the admin side of things.
But for this to work, I would suggest starting off small, work out the kinks and build from there. Do it right, do it small and then build upon it from there. Also, starting off small, if it doesnt work then it is not a big loss.