Lucky you to get to make the plans before you start. My thoughts:
If you think you would ever want a longarm, think about whether you want to plug it into a ceiling outlet. I hang the electrical wire up on my older Nolting all the time. Another thing, If you are planning on sewing or ironing in the middle of the room, put a couple of outlets there too. If you plan on inviting friends to sew with you, then take that into consideration. Have you thought about where your design wall will be? Do you plan on built in cabinets for fabric storage, a closet or open shelves? Think about your lighting for sewing. Do you want all the lights to come on at one time, or specific ones according to the area of the room you are in?