Stone raised garden bed on a slope

I want to build a raised garden bed with a stone wall. Height would be 1 foot. Since this will be in the front of the house I’m looking at “nice” stone, so not just concrete blocks. I will probably do something like 20ft by 4ft.

I’m thinking of using stone that has that “lip” on the back to make it easy to get the back setting correct. Two main questions:

1. Now I’ve done some googling around and I can’t seem to get a straight answer to whether I need a foundation poured or not. I’m in Montreal so we have pretty cold winters but depending on what site you look at even some manufacturers just talk about a gravel foundation being needed, so now I’m confused about when I would really need to pour concrete and when 2ft of gravel would be enough.

2. The bed would sit on a slope in two directions. It runs parallel to the driveway, which slopes down towards the street (I.e. the 20ft down. I measured about 5 or 6 inches down over the 20ft). But also the beds would run into the “hill” (that actually contains the septic drain field so its a hill of sand and the ground here is very very sandy to begin with). So the wall on the driveway side would just have to hold the dirt in the actual raised bed, which I assume should be no problem at 1 foot height. But on the hill side it feels more like a retaining wall. I hope this sketch shows what I mean. Slope runs down the arrows.

So how deep do I have to build the wall on that side? Does that side actually need a foundation and wall at all or can I just put a row or two of stones for looks so that it actually looks like a garden bed and not just a retaining wall, given that the hillside is holding itself right now as well?

3. I don’t need a drain pipe behind the 1 foot high wall in the front that runs along the driveway do I? From what I read so far it seems that I might just add a bit of gravel in the front behind the wall before filling in dirt especially since we have sandy soil (we have lots of commercial sand pits here actually).