How about some wood blinds on the sun room windows to control light source. I have that on my sunporch, actually fabric blinds, and they work just perfectly. You could use just three, one over each double set of windows.

It would look great, I prefer the medium tone to the very dark ones.

I go with the sunroom, too, and here's why. You can build a shed for cheap at some point, and until then you'll probably keep one car inthe driveway, and all the bikes and basketballs in the garage along with the yard and snow tools. The sunroom will make a great playroom while the little ones are little. I've seen that sunroom with nothing in it but a low-pile play rug and Lego. Or balls. Or plastic hockey sticks. Or those big Little Tykes (slide, trikes, trains) Or Hot Wheels. Or dollhouses. Or art projects (easy-to-clean tile floor). Usually just one or two of those. But a great playspace, near you but not, outdoors but not. After they are done with those types of toys, it can be dining space and added living space. You don't need the shed until Boy #1 gets a car. Oops, didn't mean to scare ya lol! Upstairs, I wonder if you can steal some space from the game room to make a reach-in closet for Bedroom 2, and use its walk-in closet to expand the bathroom. 5 boys will need more counterspace, more drawer storage, and (I can't believe I'm saying this, I'm usually a 1-sink gal) 2 sinks. Downstairs, consider eliminating the study closet and adding a shower to the powder room.

Do you really want to sit in there with dirty shoes, dog food, sports equipment, etc? Mud rooms and sitting rooms don’t always combine well since mud rooms can get a bit chaotic, and a sitting rooms seems to request tranquility. If you are a neat nick, and your family members are too, you might be able to get it to work. Is that the main entry to the deck from the house, and is the deck large enough that you will use it for entertaining? It’s almost a pass-through space since the kitchen entry is diagonal from the deck slider. Do you enter the deck from the slider