let the shop recommend what to do and buy everything from them. i never recommend buying yourself then asking a shop to install it. warranty work is out of your pocket and there is finger pointing when things don't work.
running passives with a 4 channel amp is a fine approach. Dynaudio mids/woofers are also beautiful. Just get either an all Dyn or all Hertz front and rear stage - mids only in the rear. Run the front comps with the passive crossovers. Power from Alpine amp is then an easy approach.
I can tell you from experience that a MLK set (with passives) is beautiful and doesn't need to be ran active. I'll also say that sealing and deadening the front doors is required to get the most out of them.