While I'm travelling I import a selection of raw files from my Canon camera onto my iPad Pro each day.
In Lightroom Mobile I have created a new collection and added the photos from the camera roll to this collection.
I do some basis edits in LR mobile and share these photos with friends and family.
Back at home on my MacBook I can see this collection in LR Classic CC under the "From Lightroom Mobile" folder.
These photo's are stored in a certain folder on my harddrive (set in the preference of LR).
Next I want to import all my photos from the memory card into Lightroom Classic CC.
Note: during import I apply a preset for renaming my raw files (initials + date + imagennr, eg. ABC-20181017-5601);
What is the recommonded workflow to :
1. prevent duplicate photo's (photos already imported on Ipad and same photos from memory card)
2. keep the edits of the photos processed on the iPad
In this case, I think you should first wait for sync to complete, so you know all your selected raw files have arrived safely. Then do the import, relying on Import's duplicate checking to ensure you don't bring in the same file twice. I think it's actually easier than you - quite rightly - fear.
In this case I would rename files after importing, not during import. That helps LR's duplicates checking, and also means your LRiOS-imported and Classic-imported files are in the same naming convention and correct sequence.
re 2, that happens anyway, so no reason to worry.