Whoa, you ask a lot Justin
We currently can't do animated skies and realistic water - wish we could
On the topic of textures I can give you some advice.
"Too tiled or too stretchy" - yup, that describes one of the main problems with realtime textures.
A good example of how to improve this is found in the desert - the cleft.
The desert texture is actually two texture layers one really stretched, and one detailed (has much alpha, and mostly puts in the pebbly detail).
You can do this in blender/pyprp too. You need to make a basic uv/map that can be used for both textures first.
Then you go to the materials tab, and make sure you have two texture layers (image).
In the materials panel, you have for each texture "a Map input" and a "Map to" (or similar names)
In the map input, you can scale the individual texture up, in both X and Y directions, so you can make one texture very stretched, and the other very detailed.
(You can use the Z value, to add a multiplication factor to these values, like - if Xscale = 10, and Zscale is 2, the real scale used for X is 10 X 2 = 20)
One day I ran through the cleft for the fiftieth time, and found that uru held no peace for me anymore.