Welcome to Canreef! You're starting off right in the hobby and doing lots of research and asking questions first, wish I had done more of that as I probably would have done some things differently myself. There are some very knowledgble people here so it's an excellent resource of info.
I'll try to comment on some of your questions right away, others with more experience can fill in details and correct me if I'm wrong.
I don't think a window 14' away should pose too much of a problem unless it puts direct sunlight on the tank, even then it may only be a problem in the summer and a curtain solves that. Using the 75 for a sump for a 120 or 180 is ideal, even a luxury!
I'm using a 45 as a sump for my 120 as it was the biggest I could fit in the space I had. Quite often the sump and fuge are together as one unit although I know of systems where they are seperate. My 45 serves as both by siliconing baffles in the tank to create seperate zones. My fuge is on one side and my DT overflow drains on the other side, my return is from the middle. A lot of ways to skin a cat (who came up with that saying anyway??)
With an in wall build and seperate fish room you can get a real nice set-up going. Do some carefull planning and you can make maintenance very easy. A couple of things I did which really helps were as follows:
I plumbed a dedicated water supply line close to my tank for my RO unit and also for cleaning stuff like my skimmer cup, I also plumbed in a small bar sink.
Using a RV water storage tank with pump to store mixed saltwater.
Smaller tank mounted above the DT for atomatic top-up
These things alone mean I never have to move a bucket of water again...something I hate with my freshwater tank.
Dedicated GFI circuit (wish I had two, but the panel box is full)
Just some ideas to think about, as far as plumbing goes there are all kinds of ways to do it sop you have to make some decisions on things like overflows, closed loop systems, internal or external return pump, etc...