Good South West events are the TriFerris ones in Cirencester park. Long and short courses depending on what sort of a challenge you are after. They were giving shot glasses as the finishers reward last time I did this race 🙂
As your first race, use the shoes you are used to. Trail shoes are good for the Tomac events as there is a mix of slippery trails through the woods, and some road sections. Then switch into your normal MTB shoes, then back again for the run. Don’t bother with elastic laces, depending on the conditions, you get your shoe stuck in the mud, so tight laces are a good thing to have.
Don’t use a bike with poor mud clearance as this is sticky Cotswold mud… I’ve seen people have to stop on the downhills to clear mud from tyres before.
Don’t worry about changing clothes between sections – pick your outfit and do the run and cycle bits in that (exception being the helmet…). Some people run wearing their cycling gloves.
Get some practice in beforehand at running after a bike ride – ven if it is just 5 minutes every ride, then you get to know what your body feels like combining the sports.