Get whatever shoes you want. Mountain shoes/road shoes, it doesn't matter as long as they do what you want and you like them. I have mountain shoes and Speedplay Frogs on my road bike.
Buy the shoes and pedals at the same time. By buying the shoes and pedals at the same time, you can be sure they match. If your LBS can't make the cleats fit the shoes you've chosen, you can make the decision right there how you'd like to proceed. (different shoes or different cleats/pedals)
Frogs are often recommended for folks with knee issues, because they are passive release (no pressure required) and have huge float (20 degrees). There are no moving parts or springs or anything on Frogs. It's like a pickle jar (pedal) and a lid (cleat). Extremely simple.
"If Americans want to live the American Dream, they should go to Denmark." - Richard Wilkinson