First the blocks you are describing seem plenty big enough for a 28" wall. You are talking about 7 blocks high. I would personally use a taller block but I like making the install go easy. Smaller blocks I believe are more work.

I have used this glue - http://www.liquidnails.com/products/landscape-wall-adhesive-LN905

However I only glue the caps - top layer to the second to top layer. The other layers shouldn't need it. Either way the glue will last only a few years if you are in a temperate climate.

I also would not install blocks without a lip for any area that will be walked on that is that high. Having a lip or not really matters with the amount of frost your region has and the amount of traffic in the area.

First the blocks you are describing seem plenty big enough for a 28" wall. You are talking about 7 blocks high. I would personally use a taller block but I like making the install go easy. Smaller blocks I believe are more work.

I have used LIQUID NAILS® Landscape Block, Stone & Timber Adhesive

However I only glue the caps (top layer to the second to top layer). The other layers shouldn't need it. Either way the glue will last only a few years if you are in a temperate climate.

I also would not install blocks without a lip for any area that will be walked on that is that high. Having a lip or not really matters with the amount of frost your region has and the amount of traffic in the area.