Im an experienced painter/modeler but im at a loss as to what to base Legion with.

I usually do a mud/grass/tufts approach but im thinking I want something with more of a sand/tufts look (without being a desert/tattoine basing)

any input?

A good question, and something I prevaricate on significantly when painting models. The easy solution for me is a temperate environment—either fields or woodlands in a kind of 'anywhere Europe/Nth America' style environment—because there always tends to be more terrain about for that. But I have started to consider painting some of these models and basing them on either a swampy or muddy landscape. About ten years ago I painted a lot of beastmen for WFB up and based them as if they were on grassy foothills with lots of loose shale lying around. I really liked the look of that and no longer have those models, so I might recreate it.

Basing, to me, is as important as the paint job. Spending a lot of time working on a good base is always worth it.