This is a real nice looking map
There is one thing that for sure says "First Map" and that is your river system. As long as gravity and physics are at least generally working the same way in that world as they do in ours there are some basic rules that apply to rivers and lakes...
Water flows down until there is no way out, at that point it will form a lake.
Eventually all water and therefore all rivers will end up in the ocean (except in some very arid area where all the water evaporates)
Water flows together, smaller rivers join, large rivers rarely split (except around smaller islands or in river deltas and that are, in geological terms, pretty unstable situations)