Tirpitz is probably a simpler conversion than the KGV, since it has a one island superstructure which lends itself to sitting over a coaming surrounding a nice big hole in the middle. Handy for keeping splashes on to the deck at bay and away from the insides if no holes are left under the turrets.
It might be a worthwhile exercise to get an Airfix Bismark at 1:600 to practice on. That would give relatively low cost insights into model boats and how to convert a static plastic kit into a working model. While it could be radio controlled, it doesn't have to be.
In either case, stability is not a problem with a model battleship. Not only wide, but very deep and lots of space low down to put the heavy stuff. The real problem with battleships is that the deck tends to be very close to the water for a very long length meaning that quite small waves tend to wash over easily.