Ok, jsut read the post about lithops and understand the error of my ways there. Still am confused with moisture and repotting cacti in general. Here is the plant i have on the way.

Those are not cacti, first of all.. those are Euphorbias (Euphorbia lacteas is my best guess). And you wanted to put them in a nicer pot? Sure wouldn't put them in a larger pot (maybe a bit deeper is all). For most succulents, I just pull them out of the pot they're in, and put them, root and soil in the new pot... only time I recommend washing roots is if there is something wrong with the soil or roots themselves (like root mealies, or rotting roots, or muddy, sloggy soil, or you are root pruning to fit something in a smaller, shallower pot). Why damage roots more than you need to? As for when to water next, kind of depends on your climate and situation... in California, outdoors, I almost always water immediately after repotting, though more to make sure the soil fills all the spaces well rather than giving the plant needed moistures... most times I doubt it really makes a difference if you water immediately, or a week later, but I still like to get it done right away... I might chose to do so differently in winter, or indoors, where plants are growing a lot more slowly.

Hey, thanks for the info! No, i bought the euphorbia online and it will be arriving bare rooted today. Yes, to my earlier point I now realize it is not a cactus. I thought it was a columnar cacti until i did a bit more research.

Since i have been slowly transitioning all my plants to 511 from crappy potting mix, they generally do have soil issues in the root ball.

Thanks for the tips about watering. I think the lithops issue i had was not a 'watering too soon after repotting' issue.