Welcome aboard. My two cents to get you started...
For clouds HDE by Diaz can't be beat, easy on FPS too, a BIG plus for my set up.
For water try those by Bill Lyons or one called Vilk's Water (vater.zip) I think that is what I have up now. It seems to have virtually no detectable patterning. I think Vilk did the "morwatr" set mentioned earlier. Also try a wave effect (newwave.zip) by Michael Young. And better coast waves by Luiz Alvarenga (morwave2.zip)
For mesh search rhumbaflappy here at SOH. This tireless soul did pretty much the world, makes everything soooo much better.
Then there are scads of beautiful sceneries of small fields for bush flying, alone and in sets.
There are good ground textures already mentioned. I will only add that the file "detail1" in scenery/world/texture makes a big difference. Some will cause snow to be spotty, others strike a nice balance between whitish snow and summer dirt. I'll try to ID the one I use.
And ask if you need help where to put all these goodies.