I have a bottom center drain on both kettles. They are the primary drains hooked up to the pumps, and I think they work great. Having another port is not an issue, though. You just plug it up when not in use.
If you go slowly with the pump under the mash, there is no issue with sticking the mash. I have yet to do it, including some very high percentage wheat batches. I do use rice hulls as insurance.
As for the whirlpool, I have that fancy whirlpool arm that works quite well and I never end up using it. I simply place the hose from the outlet of the pump into the keg against one wall. It spins everything just fine. Then in stead of letting it settle, I rack out as soon as it is cold through a filter bag. Done quickly and easily. I would not whirlpool and then filter; pick the one you like and go with that.