Hey, fellow Southerner here!!
As others have said the Southern Welsh and Shropshire races are your bread and butter and I've been made to feel so welcome at any I've been to!! Remember to keep checking the WFRA site as well as the Mynnydd Du and Mercia club sites for races in their areas.
One other tip for me is to take out a subscription to Trail Running Magazine. As part of the magazine package you get a years access to OSmaps online which has proven invaluable to me so far in the few months I've had it!
Another Reading runner here; I live in Caversham, and have spent the winter running up and down the edge on the Chilterns and enjoying muddy footpaths. Not exactly fell running but it's a start. I would like to do more in the future ... very pleased to have found these forums (fora?) more or less by accident, and would like to find some races suitable for beginners so thank you to all for the interesting suggestions on here.
Also worth thinking about southern coastal paths for training and possibly races too. I have done quite a bit of running on the Purbeck coast around Lulworth and Swanage and there are significant ups and downs, which are more severe than you might imagine. loops inland allow circular routes to be made.
There's a couple of 'official' fell races around the south coast, near to Exmouth/Sidmouth area. I'm sure at least one of them simply follows the coast path.