Right of the bat I would say that rivers could not originate from a sea and flow outward, being that the location of the sea would be the lowest point in the terrain, and as far as I know water only flows into oceans and sea's, except in cases of things like tidal bores, where the salt water flows back up the fresh water course due to tides....but it really made me think, as sometimes what we think we know is not always true, so I did a google search and could not find any reference of rivers out flowing from a sea. but as there are sea's below "sea level" i could be wrong. The definition of a sea though is a saline lake that lacks a natural outlet
Large fresh water lakes could have outflows though. The great lakes are connected by atleast 5 rivers, and are called inland seas by some, so it is possible to have your seas have outflows. So if your terrain suits an eastward and westward flowing river, it may work.