I might get 2 mini rexs (bunnies) in a few months...i want to keep it outside?

I want to get 2 mini rexs and keep them. Out side I would take them out and play with them at least every other day mostly everyday will flys be a problem I have to huge cages, one is filled with dirt and the other has an open bottom for grass I was thinking grass, I would move the cage every week or so, so they don't have 2 much poop everywere, I have 2 small dogs (japenenese chins) they wouldn't get into the cage because I had chickens before and I had no problem with predators getting in, would my small dogs try and kill the bunny or will they become friends? I no they will probably try the first option but they are very small dogs 10 or 7 pounds. Would I have a problem keeping the bunny's cool enough were I live it never goes below 70 degrees and it usally goes up to 80 in summer somtimes 90 how could I keep the bunnies cool there is an area were bambo is wraped around the cage for shade...would I have problems