Hi Sharky. another 'Hello' from Sussex.
Re getting out onto Byways, if I'm correct in my thinking......(and I may be wrong here,
) your bike Yam yz is a MX model ? If so, and has not been made 'road legal', and carrying a registration plate, to use said legal vehicular rights of ways, you would be breaking the law.
Apologies if I'm trying to "teach you to suck eggs".........
as for kit, baring essentials, I think everyone has their own opinion; for me, I dehydrate easily so carry water and wear a camelback bladder, carry a first aid kit, (and bog roll/wet wipes
)..high viz vest, head torch and other bits n bobs.....but then again I ride a quad, so have a little more room to carry stuff.
As to hooking up with others near you, have a look in local groups sec (in members sec)
All the best