Hi Larky,
Welcome to the big grin fat bike family, the most interesting thing I found was that so many people want to talk to you about the bike!
I am local to you, Wickham, and as others have said simply ride the same trails but you can also ride trails that you would avoid like plague in winter normally.
QECP is a hoot, but even more so you can ride around the Whiteley Woods tracks all year (all your skinny tyred mates will drown in WW1 style mud), there is a great 10 mile loop out the back of QECP (used to be on Hants CC website but they recently started charging for it, bastards!) but a google should find it and that is a mud fest in places but a great mix of everything.
If you want a guide for that one or another fat bike to ride with holla as I need any excuse to ride more 😉
Fatbike is for life not for winter 🙂
James