Answers

Any insulated siding should suffice. Vinyl siding with a backer board or insulation should make the room usable.

Hardie Siding is effective as well as it is more durable but is more expensive.

Make sure to find the a highly energy efficient window. There are several quality manufactures in your area.

Best wishes.

Yes. You can paint vinyl shutters. Clean and then use an acrylic latex paint made specifically to plastic materials.

Spray Foam. Much better insulator and fills any gaps that might otherwise be missed.