I'm moving to my new house at the end of March and am trying to decide what to do about the vegetable garden that I don't have space for. All I will have is a sort-of passageway that is paved with bricks. But it's quite wide and I'm thinking of building a raised bed along one side that is the whole length, out of bricks. The area gets plenty of light too.

I have a couple of questions/concerns though, but here's basically what I'm thinking of doing:

1. I don't intend to pull up the bricks (underneath the bed itself) but will ensure there is sufficient drainage. The passage is on a slight tilt/angle so shouldn't be a problem. Anyway, there is also only building rubble under the bricks, so there seems no point.

2. I'm wondering if I need to seal the bottom and inner sides.

3. I intend to put a layer of stones in the bottom, also to aid drainage.

4. There will be 3 or 4 sections separated also with a brick wall to add strength to the structure and also to be able to rotate the crops.

5. I'm not sure what the minimum depth should be, especially if I intend to grow carrots and onions as-well.

Any suggestions/advice would be appreciated.
Thanks
Mozie