depending on what dry verge you use
Russel dry verge over hang the lath 50mm
Marley and klober 35mm
But I'm sure most dry verge will come with its own spec
No you won't need mortar behind
Also the dry verge is maintenance free any probs get in touch
Most definitely not im a qualified roofer with over 25 years experience, never use door knockers £900 to Rebed ridges is a rip off they probably won't even Rebed them they will just repoint over the existing mortar steer clear