Thanks!
I already found sufficient answers on the WoT forum where I asked these same two questions.
This is more than enough for me to go on for the schurzen mounts, and the anti aircraft covers were, as I found out, both factory applied on very late JP's and field applied as well, where the crew would just cut up some schurzen plate and weld it over the vents on some posts. This 'field modification' idea appeals to me. Plus, it means that I won't have to be so accurate with measurements either.
Thanks for the replies, Painless and Tom. That is a wonderful build you've linked, Painless. I'm gonna go study that too.
JagdPanther / Leopard 2A6 / StuG Ausf. G / KV-2 / M4A3A4 / MTLB / 2.5 ton truck 6x6