This is the main website I use for mods other than Ultra Pack, which I haven't upgraded to UP3, yet. (Am still at 2.01)
Special Aircraft Service - Index and one that I haven't used as much (imho, I think its a former shell of itself, it used to be All Aircraft Arcade before the site collapse)
All-Aircraft-Simulations - Index
And to answer your question on lansdcape textures (I'll post some mods later), In your Il2 install directory find the config file, open that up and find these of entries of which there are two of each under categories OpenGL and DirectX, only change the one that you are using for the game.
Mine for example
HardwareShaders=0 (Put this on 1 leads to water with higher pixel shader Appearance and Visibility of the landscape and new trees
VisibilityDistance=3 (keep this on 3 for max visibility)
Forest=2 (Keep on 2, I think its the max)
LandShading=3 (Keep on 3, as is max)
LandDetails=2 (2 max again)
LandGeom=2 (change to 3 = High quality, far distance with gradual fog fade)
TexLarge=1 (1 is max with large textures)
TexLandQual=3 (3=max)
TexLandLarge=1 (1=max)
A guide to the config file if you want to do more tinkering
All-Aircraft-Simulations: Topic - De-Mystifying the Conf.ini
Now with those set, thats the maximium you can change the landscape graphically with stock settings of the game. (I think!)
I'll post some mods that I can find soon, I assume your using 4.101 or 4.11 in conjunction with UP3 am I right??