It always helps a lot to clarify from
unitednations having lot of exposure and practical experience. It's critcal to know ahead what to send and what NOT to avoid trouble later.
I can not imagine how much time you spend to research on these issues before you give any advice.
Like UN said before, (reading instructions of 485 filing), it is not mandatory to submit employment letter and medicals for other categories like fiance', asylum, refugee, derivatives,.... So, at Prima facie stage, folks wont do that detailed scrutiny for them.
For initial acceptance of 485 petition, one has to submit minimim, copies of
1. 140 receipt # to claim eligibility to file,
2. Full PP , I-94
3. 2-photos
4. G-325a
5. Fee $385 for each application (does one has to submit for all derivatives too or can be filed later at RFE stage?)