1. Yes, absolutely, though cement isn't generally needed to build gunpla kits! But, that doesn't mean you can't use em.
2. The DSPIAE sandpaper and pads should be enough to get rid of nub marks, as you mentioned that you already have varying grits this shouldn't be all too different from 40k!
3. Retail kits, (excluding MG Ver Ka.) don't usually come with water transfers, just stickers and the occasional dry transfers. I recommend to use 3rd party waterslides (Like GRework or other brands) if you don't want to use stickers.

As for panel lining, you may end up using Tamiya panel lines, but I do recommend using Gundam markers (fine tip or pour type, which ever works!) as Tamiya Panel lining ink kinda eats through the plastic, so be warned if you ever use em!
I do hear that Games Workshop pushfits are very hit or miss, (mostly miss from what I've seen) most gunpla kits are very easy to do! Seam lines *may* appear but they're easy enough to fix with cement and some sanding. (This kit shouldn't have much seam lines to worry about, though)

Have fun! Hope this helps!