TL;DR - No need to be able to play with your eyes closed.. Unlined/Lined are both great. Make sure you have great left-hand technique already. Vibrato will come.
I've been playing fretless for... 18 years. I've had both lined and unlined instruments; I care more about what wood the fingerboard is made from than whether or not it has lines. Side dots are critical, but I've never seen a fretless bass without side dots. There is no reason you need to learn by "feel" and never look at the fingerboard... the dots will always be there. Everybody looks at the dots. For anybody to say you need to be able to play blindfolded is, to me, absolutely ridiculous. We play classical instruments by feel, but not electric bass. I mean, sure... you don't sit there and stare at the neck the whole time, but when you shift, or go to solo or something, you'll look at the neck, and that's perfectly fine.
I think many of the problems most people have with fretless are because, in my opinion, they play fretted instruments incorrectly. Or rather, perhaps not incorrectly but... carelessly? Or maybe they just never really focused on really solid left-hand technique. As big_fundamental mentions, you should be playing *just behind* the frets on a fretted instrument... as close as you can get to them, really. For new bass players it's not so important, but once somebody starts really practicing and focusing on quality of sound, playing close to the frets is critical to eliminate buzz, pitch inaccuracies, etc. So, then, moving to fretless isn't such a weird feeling if you're used to playing just about on the lines anyway.
Further, intonation shouldn't be too much of a concern nor something you should really need to practice. If you already have solid technique with your fretting hand, there's no real difference on fretless other than a few odd things here and there (double stops, etc.). You'll know really quickly if your fretting technique needs some work. For instance, if your finger spacing is already accurate on a fretted instrument, playing fifths, thirds, etc. on fretless is exactly the same and should be nearly perfectly in tune the first time you try it. If they're not, it might suggest that you just need to practice your fret-hand technique; it doesn't have anything to do with fretted vs. fretless, it's merely left hand technique.
The things you *will* have to practice are the little things like vibrato and stylistic things. My biggest tip for vibrato is... don't do that weird shaking thing some people do; you want to roll your fingers from side to side. It'll come. Don't worry about it on the first go.
Other than that... just do it! You'll enjoy it.