Regarding texture sizes:
Let's say the 2048 pixels represents 80m in real life, that means that it's a 'real-life' resolution of 25.6 pixels per metre. If you therefore set one blade of grass to be 1 pixel wide, you end up with a blade of grass that is 4cm wide, which is clearly silly.
The best way to do this would be to have a 1024x1024 (or maybe even 512x512) texture to represent the 'shading' on the grass (i.e. the way the mower rolls it and makes it look stripy) and then have another grass texture which has all the detail, which is then tiled and blended. This is called detail texturing, and the idea is that the detail texture is only shown when the camera is close to the object, and ignored when far away as you wouldn't really be able to see it very well from long distances anyway.
The problem with this is that you might well need to split the ground surface up into several polygons rather than one large one, so that each polygons distance from the camera can be assessed, and the detail texture applied or not. There may well be automatic ways to implement detail texturing in the tools that LM is using, however, making this easier.
What most of you have been doing so far, is designing grass a grass texture for the whole field, but making the actual blades of grass look right for about 4:1 scale, when we are actually talking about 80:1 scale, roughly. This will mean your grass blades will look silly when blown up.
If detail texturing is not being implemented, then the best thing to do is not do grass blades, but imagine what the ground would look like from 100 feet in the air, and make that as a texture.
We really could do with more guidance from LM/JK on this.
