O Fallon, MO
The wire from menards will work just fine. I would use 1-1/4" conduit for the #6 thwn. I would use 2" conduit for UF cable.
I would also drop a spare conduit for phone / ethernet / intercom (or whatever).
Conduit is cheap, time is valuable, and trenching is expensive.
Code tables can be overly optimistic when it comes to conduit fill tables. While technically code allows you jam X number of wires into a conduit, the reality is that a trade size or two up will make life a lot easier. When using code as a reference, remember it's the "bare minimum" that you can get away with.
You can probably get your materials much cheaper from an electrical supplier. Retail prices on electrical items are a rip-off. We don't have a Menard's here yet (they are still building it). But if their prices are along the same line as Lowe's Depot, then they are probably overpriced too.
If someone refers to herself / himself as a "guru", they probably aren't.
I found a place at half the per foot price of Menards so good suggestion.
One final question, Does the ground wire need to be #6 or can it be a #8 or #10? The supply shop has black, red and white in #6 but not green.