Converted to the english units many of us are familiar with, that's 12 pounds of extract in 6 gallons (or 10lb per 5 gal batch equivalent).
Rule of thumb is 37 points per lb of LME per gallon and 45 points per lb DME.
OG target for 6 gallons is 1.080. Given 80% attenuation (which is very generous), that's a FG of 1.015-1.020 for a rough ABV of 6-6.5%.
You will not need a high tolerance yeast at that strength. Pick a good ale yeast that will give you some flavor along the way. I've personally had very good success with WYeast #3068 and #1010, depending on what flavor you're going for.
Also, you didn't mention any hopping rate, spices or specialty grains. I find that wheat extract is a bit "weak" in the wheat flavor department and I like to supplement with some specialty grains. If you're making a dunkel, stick to all pale wheat malt (which is likely all you'll find anyhow) and use some of Weyermann's chocolate wheat and dark wheat for color. For 6 gallons, 1# chocolate and 1/4# dark should give you about the color you'll need. A minimash of another 3# wheat malt and 2# of 2-row will let you skip the DME (of which "wheat" can be hard to find) but you'll tack 40 minutes or so onto your brew cycle.
For hops, I tend to go light and noble. Figure about 3 ounces of Hallertauer, Saaz or equivalent in the whole batch, keeping it around 15 IBUs or so, and a bit more for a dunkel. I've had good success with star anise as a spice for American wheats but for Bavarian style I skip the spices completely.
Poke around and look at some other recipes before you settle on something. Good luck.