Caveat: My surface grinding knowledge is limited, however:
Nice, accurate grinding of long parts is difficult with hand feeding and no coolant. BUT you can always use more "table space" for setups and additional in-situ measuring. Go with the vice that provides the most area while still being practical.
I'm not sure about the magnetic on/off elements, but the table surface should be relatively easy (in fact, almost certainly necessary upon installation), to true up with the grinder itself. I'd suggest that it not be the first thing you try to grind though. As long as it's flat enough to hold a part well, forget about how parallel it is to the axes and just try surfacing a few smaller parts first, maybe in a small grinding vice. Then once you get a feel for the machine, go at getting the vice flat/parallel. If, as you improve your skills, you find that you didn't do it as well as you thought, just do it again. Take off the absolutely minimum required to get a true surface. If there's a spot that's really bad and you need to go really deep to clean it up, think about whether you can live with just avoiding that area. It will be fine if it's out of the way.
I've only used the permanent magnet type, which I think work very well for small machines. One benefit is that your work doesn't get launched if you have a power failure.
As I'm sure you know, but I'll remind you, YouTube is your friend. Suburban Tool has a couple of surface grinding videos with nice little tidbits of knowledge thrown in there.
One more thing: DUST! Obvious, but I wouldn't even try to put it in my living space or near other nice tools without really good dust collection, or perhaps coolant controls it well enough - though no fist hand experience with coolant.
I'd love to get one myself, but do have access to one at work. Unfortunately it does not get treated like the precision machine tool it is supposed to be.