Keeping it simple, any cellulose sanding sealer will be fine for sealing and grain filling the hull. It is quick drying (20 minutes or so), which allows for fast re-coats. I would suggest sanding between coats to cut down the fibres in the timber, which will become noticeable. Three or four coats will be ample. You can then overcoat with any preferred primer, finishing with a top coat of your choice. I have yet to encounter anything which racts with a cellulose base coat, so you should be fine.
Making it complicated, I have used shellac sanding sealer before, very good, but a far slower drying time (about 45 to 60 minutes), and it does require methylated spirits to clean the brushes.
I have also added talc to cellulose dope, this works, but limit it to about a teaspoon in 250ml, or it all gets a bit thick!
I have recently been using epoxy laminating resin, either with microballoons as an additive for sanding down (like laying on thick varnish, much sanding required to get a smooth finish), and with glassfibre woven cloth (very good for sealing everything to a tough finish on a foam model).
Of all the above, the top one is the easiest option, and for a newly built hull, probably the best option.