Benjy,
On the subject of RN Sqn numbers the same seniority rules apply, hence 800NAS should be the first RN Sqn on F-35. This is why 800 was the first RN Sqn to form with GR7 at Cottesmore. Plans were made for 801 to form later but various political wranglings prevented this from happening and led to the creation of the brand new and numberless Naval Strike Wing (NSW) before an eventual return to 800NAS. For note operational Sqns usually are 8xx and training Sqns are 7xx. 899 and 848 are OCUs but also have/had an operational role.
However, the F-35 is a joint asset under 1 Grp RAF so the first (and possibly only if you believe some reports) Sqn will almost certainly be an RAF one. 1(F) Sqn may be held onto for this, particularly if we go back to the STOVL F-35B due to it's Harrier past.
There was talk of the F-35 OCU being 899NAS when 20(R) Sqn was still in use as the Harrier OCU but again I feel the chances of this happening are slim to non-existent.
Hope that helps.