Garlic doesn't require rotation as it isn't a plant that is usually bothered by pathogens that overwinter in the soil. Some say that if you continue to replant what you grow the garlic 'evolves' to grow better in your soil year after year.

5' spacing is fine and yes, they can be 'grid' or sq. ft. gardening style planted.

Garlic is both shallow and deep rooted. Unless you are really careful when digging the garlic up you will only ever see the thicker roots that are usually a couple inches long. The roots go deeper, but they are super thin and fragile. How high to raise the bed? Well it doesn't matter that much. I would suggest 6" with the soil underneath being preconditioned with compost being worked into it to 6" and that should be plenty. In other words shoot for about 12" of quality growing depth in total and that should be plenty. I have seen garlic grown in containers with less soil depth and they did fine though.

For best results keep the garlic growing (same with onions) and that means make your planting mix well amended with compost and/or organic (cause they are very slow release) fertilizers. Additionally supplement the garlic once a month or more often with additional feedings and keep the soil moist. Dry soil results in lost growth time.

I made raised beds this year for the first time, and will be moving my garlic to a couple of them this fall. The four foot width worked well for me, and the 10" x 2" (rough cut) sides were perfect, just high enough for the wheelbarrow to empty over. I worked the soil beneath the beds before building them to provide additional depth.

I am planting my cloves at a variety of spacings, though 5" will be by far the most common. I will probably provide them with more space between rows than within the row (this is to provide more light), as much as 8".

I will probably continue rotating my garlic beds, not for the garlic, but to give my pepper and tomato beds a rest as I have problems with fusarium wilt.

That should read 8" by 2". The wheelbarrow fits perfectly over an 8" side. Sorry.