Brick and mortar raised flowerbed

I am repairing a brick and mortar raised flower bed. I'm pretty sure it's about 50 years old or so.
I thought I would just reset a couple of the bricks where the mortar had disintegrated and repoint some of the crumbling mortar. When I started cleaning out the mortar I discovered that two entire courses has to be removed because the mortar joints are totally degraded. The mortar is very wet and crumbly.
I have absolutely no experience with masonry so have more than a few questions:
1. How clean do the bricks need to be before mortaring them back in place?
2. The bricks have eight (manufactured) holes all the way through and the top course of bricks was finished off with cement. Some of those bricks are still held together with the cement. Can I reset them that way or do I need to break them apart? I don't plan on removing the cement from the top of the bricks as I'm pretty sure I couldn't get it off and it seems quite sound.
3. Should I try to do something to keep the soil away from the bricks so that they won't be wet all the time? Poly behind the bricks?
4. How long should I wait before I fill the bed back up with soil?

Brick and mortar raised flowerbed