Add marshes near Minsk area just like on this screenshot, or maybe a little
east 
, because these resources (cow, horses and wheat) are usually taken by Poland (thanks to its UP), so settle Minsk is useless waste of

and

, but these marshes can improve gameplay and make Russian-Polish wars more interesting.
Add independent city with strong garrison, walls and castle that will not flip to the Ottomans to represent orthodox population of this area (
Armenia,
Georgia).
Add 1
wine near Odessa, add 1
wine near Caucasus.
Add one hill and replace some deserts with plains to buff this region. South Caucasus should be grasslands.
Flood plains near Astrakhan - have a look at
map, and you will understand why I think it should be added. BUT, there will be one problem - Volgograd will be kind of megacity with a lot of

and

. Maybe reduce flood plains from two to one?
Move fish near Constantinople to north, move clam to east, so possible new cities can take this fish. But my plan probably will not work, because Constantinople has very strong culture. Maybe add one fish near Odessa?
Add 1
iron on the desert near Crimea to add more

for possible Ukrainian/coastal cities.
Make some changes in stability map.
Also, is it possible to change third UHV (have 5 communist friends) to this? Control European part of Russian Empire by x (1800?) year/allow no foreign cities in European Part of Russian Empire by x year. This will force the player to fight with Sweden (Finland, Baltic states and Karelia), Poland (Lvov and Baltic states) and the Ottomans (Caucasus, Crimea)

.