My start was in upright, and I played Fretless exclusively for a number of years so here's my take.
Rounds vs Flats. On rosewood, I'd say flats only. Rosewood is a comparatively soft wood and it will wear.
On Ebony (which is a harder wood), Ebanol (a synthetic) or an epoxied board rounds are just fine. Make no mistake however, they WILL wear at the fingerboard. I played an ebony board Carvin Fretless with rounds for 4 years almost exclusively and off and on for a few years after that. That's quite a bit of use and it shows on the fingerboard. You can really see the markings from the strings. It hasn't gotten to the point where it affects the playability and theres only a few spots where you can feel much difference under your bare fingers, but wear is happening. Just know that wear does happen and in 6-7 years of heavy use, even an ebony board will need to have the fingerboard dressed by a luthier. Not a huge deal, but it will happen.
Also, note that some strings are much more aggressive than others. Stainless steel rounds are going to bite at the fingerboard more than nickel steel. If a string has alot of bite on your finger (I'm looking at you Roto-sound) it's going to bite at your fingerboard.
As for unlined vs lined, I say go with what you're comfortable with. I go with unlined because it pleases me visually and the side dots are enough for me. Also, if I'm playing fretless on stage, I want folks to know it. However, if you find it intimidating, then there's nothing wrong with lines.
Good luck and I hope you enjoy the fretless experience.
My last bit of advice would be that when you are learning fretless, do as much of your practice as possible on the fretless, even if you gig on other instruments. I'm getting back into fretless now and my fretless gets 80% of my practice time.