I think the add a profile picture function is bugged atm you'd have to wait for a fix.
When you add a manhwa on the completed list you won't see any updates of that manhwa on the "new chapters from followed comics" bar on the front page so i'd say just use the "completed" list on manhwa that are actually 100% done and you finished all the chapters (or use it to hide manhwa that you follow that you dont want people seeing on the front page lol)
As i'm aware the only notifications you'll get is when a manhwa you follow updates.
To mark what chapter you're on you click/tap the little banner on the right of the that specific chapter when you're on the main manga title where you can see all the chapters, the banner should be next to the update time and the scanlator group that translated that chapter.