Hi Bigjim,
With regards to what bike you should come on a RSF ride just come on the bike which you most comfortable on for going off-road on! The club national secretary rides just normal touring bike, I ride a Trek Hybrid and other members use mountain bikes but end of the day its down to personal choice what most comfortable going off-road on!
With regards to terrain 'The Rough-Stuff Fellowship' is off-road cycle touring club so on some of the rides we may stay on the tarmac for about 75% of the ride, like two South Lakes Group rides each month which start near Lancaster.
You most welcome on any of the rides in the north west of England, we only ask people to join the club after the second ride out with the RSF.
with regards
Simeon