Does this too have a built in bra?

No, it’s just made out of two layers of the same thin, stretchy, white fabric.

What would be the best size for 36DD? 41" bust

Depends on your overall size. I'm a 36 F and bought the large and the straps were way too long. Bought a medium and the chest fit pretty much the same because of all the stretch. The straps are still too long. Going to be ordering a small next to see how that goes. I wear a women's L usually

What bra size range does a size L equate to? (The lack of an accurate size chart is a problem; seller should add one.)

Not sure the exact answer to this but I highly recommend sizing down. The stretch is insane. I normally wear a small top. and medium sports bra. I got a Small and it's okay but an XS would have been much better

Im not sure, it didnt have a tag. Its stretchy, but the material is thick. I wear it a lot and it hasnt stretched or shrunk or anything if that helps.