The latest iteration of a spoke length calculator thats been around for years. Has a lot of retro parts in the db so very useful for this community
https://leonard.io/edd/
Also the thing that took me from building ‘ok’ wheels to ‘very ok’ wheels was a spoke tension meter. Getting the right and...
I am a member of Forestry England and cycling on the forest roads is fine with the usual caveat for awareness of other people or forestry operations. Mentioned in the trail grading bit on their website.