After your plane lands, figure about one hour to get from the gate to baggage, pick up your bags, walk over to the garage, rent the car, and get on the road.
Travel time from MCO to POR will be 30-40 minutes, depending on how much of a leadfoot you might be. It usually takes me about 30 minutes, but I know the roads fairly well. Figure on 40 minutes for you just to be safe.
Checking in could take 30-45 minutes or it could take 10-15 minutes, depending on the lines at the check in desk.
You should be ready to hit the parks by 3, and probably earlier. My typical time from touchdown till I walk into my room is about 2 hours.
Of course, then I have to spend 20 minutes unpacking my camera, water bottle, etc., locking my laptop away, and making a quick once-over of the room to look for broken stuff or messes.