Yeah, I think something similar to Baldur's Gate-era production values would probably be fine for a first outing. This does kind of raise the question of scale that you mentioned, though. I mean, Paradox themselves specialise in very high-level simulations, on the scale of nations and empires. In theory Majesty is concerned more with the mid-level scale of cities and towns (i.e, a Fantasy Kingdom), but I think in practice it's primarily concerned with the fine-scale level of individuals and communities, given that you'll have at most a few dozen characters around the place in Maj1.Doesn't have to. Moba games are quite popular. Best pov for strategy games is isometric. Isometric RPGs are popular too.
So, if, as you suggest (and I'd love to see it) you have the heroes starting at the bottom (solo/hero party) and working their way in scale up to the top (commanders of legions/ministers of state), then the question of how you appropriately represent and translate between each of these levels of detail becomes an important one.
Of course, CK is notable in that, in a way, the game is both about very large and very small scale interactions, in that power over vast estates is concentrated in the hands of an elite 'community' of nobles. But if you want to start on the grand-strategy province-level and drill all the way down to an isometric view of some first-level, fresh-minted newbie warrior dispatching a random varg in a cave someplace... then you're almost committing to writing three different games and hoping you can glue them together at the seams.
...With that said, I really want to play that game.