For the yeast, since you're wanting to essentially do a lager using ale yeast, you should probably go with something as "clean" as possible. Wyeast 1056 American Ale would fit the bill.
But, and it's a major but, you also mention summer coming up and fermenting at room temps. Even with an ale yeast, those two things really don't work well together. Remembering that the actual temp of actively fermenting wort can be 5-10 degrees higher than the ambient room temp, you're almost guaranteed to exceed the temp range of the yeast. That can give you all sorts of baddies from crazy esters to fusels, etc. Seriously consider at least a swamp cooler (get one of those kids toy tubs that your carboy will fit in, fill it with water, and rotate ice (ie frozen water bottles) in the water to keep the temps down). You can also cover the upper part of the carboy with a t-shirt or something, the bottom of which is in the water. The water will wick up and evaporate, helping out with cooling even more.