Do we just leave the front picture window without shutters?

Honestly I think you could go either way, my vote would be to add them just to pull it all together.

That's personal preference, some do, some dont.

Historically shutter widths were the same total width of the windows (for function) but that's not the case any more. For conformity and visual balance I would shutter all of your windows. In a contrasting color for more impact.

all the windows

I would paint the window frames black in addition to adding shutters on all the windows.

You could also just put a matching window box on your picture window the same shade as your shutters. Low-light plants like hostas and begonias would do well in the lower light.

You can go both ways. FYI window color is great so ignore painting advice. Most people these days, to be safe, make everything the same color. That is a huge decor mistake. You want at least 2 different colors on exterior. Preferable 3. The only thing you want to blend in are gutters. You want features to pop. That said looking at the three I would also shutter the picture window but I’m a visual girl so these pics may help. I know the width won’t be a functional width but you can still add it as bling. Considering it’s a ranch I would suggest the ones that are more plank in decor. Like barn doors. Much more trendy. Don’t use shutters like top right (tan house) but that shows you a larger window and it looks fine.

That's a matter of personal preference. My vote is, Go for the shutters! :)