The off road course is suitable for all. The tricky bits all have bypasses so if you don't fancy a section just go around it. You can drive through the lake and cross the river, that can get a bit deep, so snorkel is advisable for that. Mud run is fun, lots get stuck. They tried to stop me doing it a few years ago, saying that they weren't letting Series Landys through as it was too tough, I told them to get lost I'd paid my money. Trundled through no problem same route where a Defender had just got stuck.
Get your off road ticket from the LRO tent, it has a time slot on it. Get to Billing early and book your slot for later in the day.