Newbee Insulation Question

I live in Minnesota which can have pretty brutal winters. I just bought a 131 year old house which has a tuck under garage. Think of it as the end room of a basement level. The insulation between the garage and the basement I addressed by using some spray foam where there were clear gaps. The door is just a flat panel of wood so I'm pondering using some foam board insulation or? The real question I'm sure sounds dumb but I really have never done anything with insulation. So here goes. The "roof" of the garage is the floor of the kitchen/pantry. Joists and the boards that make up the floor upstairs. Its already clear how bad this is because while I've managed to tighten up old windows and drafty doors making the upstairs toasty that Kitchen Pantry feels like a skating rink to me in the morning. So I've pondered whats correct and whats "doable" quickly. If we start with me just attaching foam board to cover the "roof" of the garage there would be this huge air gap between the foam and the floor boards. If I did this because I simply can't get into this garage very well what with a giant pile of my junk from the old house which way does the metal side of the foam go? Or does it matter because this is such a dumb idea? If I cut the foam board to fit between the joists again which way does the metal side go? If I fit this tight (I saw a fellow cut pieces slight larger and pushed them in then used nail/screws with large plastic "washers" to hold the boards in.

If this is just horrible beyond belief because its just wrong what would be the right way to do it? If its the rolls of pink stuff do I get the kind with the paper backing and use my power stapler or do I use the non backed stuff somehow? And since its exposed to near outdoor temps am I supposed to try putting it behind plastic with tape etc? Or is the plastic supposed to be covering the joists and floor boards with the insulation hanging down from it?

I know how dumb this question sounds and the answer is probably hire someone who knows this jazz but... I'm on a very small budget and the only thing I have is free time. *Mine 24/7.

 

I would put R13 paper faced insulation between the joists with the paper facing down where you can staple it to the joist from the garage side. That would be he best for suggested insulation value for floor joist in Minnesota. If you really don't want to move the "junk" out of the way to do a good job then I would suggest the foam strips between the joists with the metal side up. Cut at a tight fit and pressed in place to hold it. You could maybe work around some of the "junk" that way. The foam has way less r value so won't insulate as well.