Need a set but not sure on how to get the right length etc.

I know the PCD is 100 so need the reduction but just the length is causing me the issue. I've had a look on eBay but there are quite a few listed for the Panda.

how thick are the wheels?

IIRC the trhreaded part of the bolts on my 100HP is 22mm. Measure how far the bolts you have now stick through the wheels you have now. Than do the same with the new wheels. Now you know how much longer (or shorter) the threaded part on your new bolts should be.

gr J