My knowledge about Tournaments and players is pretty limited, so I'll let others speak to that. I can speak at least a bit to the stores tho.
There is a small Games Workshop store in Kansas City Mo. Only has 1 or 2 tables, so gaming there is a bit difficult. But, being an actual
GW store their selection of
GW products is likely the best in the area.
There is Tabletop Games in Lenexa
KS. As JB alluded to, the owner (Phil) is a fantastic guy - extremely knowledgeable and very helpful. And as mentioned, they have a fantastic selection of games and miniatures of all types. Possibly the most well-rounded selection in KC. They've got something like 16 gaming tables if I remember correctly - plus an awesome painting lighting setup.
I've been to 31st Centure games once and that was years ago. That said, they seemed to be a fairly large store with plenty of room for gaming. Only caveat I remember is that the tables on the outside edges were a bit close to the retail areas and can get a bit tight. Since I haven't been there in forever, I can't speak to their selection of merchandise.
The last major store is Basement Games in north KC. They moved to a new location relatively recently, and their selection of a lot of things is extremely limited. Their shelves are pretty bare and the last couple of times I've been there that hasn't changed. They have a fair number of gaming tables (I think 8), but my impression from the couple of times I've been there is that they seem to cater more towards established players who have what they need - they didn't even have the basic
HQ/troops selections for most armies, and the newest box set they had was the Ravenwing Command squad. It's a store with potential, but if you don't stock it you can't sell it.
Finally, I've read about 2 other stores that are getting into
40k, but I've never been there so I have no idea what they're like. Collector's Cache in Lenexa
KS -
http://www.collectorscache.com/ and Limited Figures - www.limitedfigures.com in KC
MO.
I've been out of the hobby for several years and am just now getting back into it. If you do end up moving to the KC area, feel free to message me and we can see about getting a game together.