I don’t know if I could list the rivers, but I feel like there should be a couple of rivers coming from the north, past Mithila and Apana. I believe the major river that joins the Ganges near Apana was the Mahī. It’s not the river to the south that you have here, see this former post:
I’d suggest shrinking the scale a little, to make the outlines of the oceans a bit clearer.
Up to you. Maybe little drawings or flourishes would be better? Like some trees for a forest, or buildings for a city? But it depends on the scale.
They look good to me.
There are hills around Rajagaha, and these are important, as they’re mentioned often in the suttas. To the south also there is a rugged region known as the “southern hills”, modern Deccan. It’d be good to include these, as they show why the “southern road” went south-west rather than directly south.
As to forests, there are several that are named in the texts, like the “Dark Forest” outside of Savatthi. But I’m not sure if you have room for these. Otherwise, maybe just wait until the place names are there and put some tree in the empty places of the fertile regions, i.e. not in the deserts of the west.