You can attend any time you like and do the marked trails without a guide, but I doubt that you will see the best that Pines and its surroundings has to offer.
Forestry England have done a LOT of work over the last few years to the red and the blue trails, such that they are almost unrecognisable from five years ago. But the off-piste stuff takes the riding to another level of interest. For those with the appetite, there are some features that will challenge many and injure the unwary (just my opinion, I'm sure that none of them would trouble the serious downhillers). We had a look at a few but decided that we weren't feeling it that day.
As I mentioned earlier in this thread, I use the red blue and green to get about the place and access the off-piste features. I also try to include the best features of the red and blue, where possible. I have seen copies of one of my typical routes as recorded by others and I have no idea how they can possibly follow them later.
Six to ten is ideal, much above that and crowd control starts to become an issue. It is always easy to get lost when going off-piste; there are a multiplicity of trails and all the trees look the same. In addition, the more riders the longer the tail and the easier it is for the slower riders to lose contact with the main group. Also, all it takes is a mechanical or an off and the group is separated.
Give me a date, some idea of numbers, and the sort of day out that you want and I'm sure that I can pull something together that is more fun than the marked trails alone.