i have raised flower beds all over in the yard.
one is 140' long, scalloped and ranges from about 12" high to 3' high.
I used a self locking tera-cotta block. They are available at any building store.
They are easy to use and easy to lock in. I used liquid nails between each layer to lock em in.
I used them as a back stop for my water garden so I could build it close to the fence.
On the raised flower beds I used 6x6x8' treated lumber. I got a long drill bit and 3' chunks of re-bar. you can offset the timbers and then drill thru the timbers. I put a layer of timbers down, drilled thru and drove the rebar down till it was level with the timber and 2.5' into the ground. Then offset the next layer and drill thru the new timber, the old timber and into the ground then drive a new piece of rebar in thru both timbers and 2' into the ground. that has held to a height of 3' for 11 years. It took 26 yds of topsoil to fill the garden.
If you need to trim one of the teracotta blocks, just use a wide spade rock chisel and a hammer. Score the block all the way around. Put the block on soft ground and smack the chisel on the score mark. It will break on the score line. That way you can make sharp turns and end in a straight line.
As for a sprinkler system for it. I just used soaker hoses. Works great.