The Rus civillization eastablished itself because river travel is very good across such a wide swath there ... The Volga river stretches all the way from the north to the Crimean (or at least the smaller tributaries reach the sea in a bunch of places). So regardless, base camp should be on the Volga somewhere becuase travel with small river barges used by the early Rus is a really good way to get around and it is one of if not the key river. With a quick scan of google earth & maps it does seem to be possible to sail right from Nizhny en.wikipedia.org/wiki/Northwest_Russia, and mentions specifics. It also mentions an important bit - the Rus are in the north becuase for hundred of years (even past the game era) the key export is grey squirrel. You donèt tend to find as much of that in the south and te European demand was huge. So much so that the grey squirrel trade was important in founding the Hanseatic league, with the Volga principalities being their eastern anchor. My point there is that we can thus supply the base camp by traveling back along the export route, and that the Rus civillization is located where it is for reasons that do not nescessarily allign with a Hermetic exploration mandate.
Even if not on the sea directly, being in the south makes sense for a huge reason: exploration is very difficult in the northern winter. It makes alot of sense to be as south as possible (still on the north shore of the crimean) becuase the exploration can occur over a much greater seasonal range, conditions will be easier. Politically, this also extends the formal reach of the Novgorod Tribunal where the Theban Tribunal might someday decide to reach. IIRC the Theban Tribunal is not at all looking to expand in that direction - I think sundered eagle even said that in the last few centuries there has been a lack of interest or some such comment - but in the long term base could be impotant in Hermetic colonization, opening up Persia (which Europeans of the time, especially those in the east, do know to be great ... just Euro trade with Persia is very sporadic ... but Persian coin and signs of regular local trade are found on the south Volga route).
Plus there was the idea brought up earlier that the rest of the Novgorod covenenants are in the north - far less need of exploration there anyway. With the southern Volga position we still have access to the Rus too, but we are on the fringe this way.
Not that my Magus is involved with the setup, but I thought I would add my two cents OOC