Yeah, the island-side drawbridge has to raise to the island side, as far as practical value. As to 'why a gatehouse, then?' the answer could be that there's a conveniently placed rock in the river rapids that served as the base, and that each individual drawbridge only has to be half as long, which makes the questions of cantilevering it around much easier to solve. So, yeah, maybe keep those towers on the island side!
As for size of the island....I don't necessarily have a great concept of scale here. The fortress should be bigger than the gatehouse, certainly, so maybe a little bit more island? It doesn't have to be a particularly large island, though, so it's not like you need to make its footprint 3 times bigger or anything. I really do like the craggy rock, though!
As for architecture, I like the tiered effect of Kathrin's artwork. It very subtly suggests the later Minas Tirith without looking like it.
As for size of the island....I don't necessarily have a great concept of scale here. The fortress should be bigger than the gatehouse, certainly, so maybe a little bit more island? It doesn't have to be a particularly large island, though, so it's not like you need to make its footprint 3 times bigger or anything. I really do like the craggy rock, though!
As for architecture, I like the tiered effect of Kathrin's artwork. It very subtly suggests the later Minas Tirith without looking like it.