The props are adding up for sure.
I personally am trying to make things that have been listed as basic needed items, things I think we need, and things I want to include. Hopefully by release there won't be any basic items that taffers ask "why don't you have?"
Hopefully it will be more like T2 is now, "I would like this specialty item for my mission, anyone want to make one".
Our aim is to release a full package that FM's can be created with without having to resort to custom content. But I know this community well and it wouldn't suprise me at all if the first unofficially released mission has some kind of custom content in it, even if only a texture.