Hey Candyman, welcome to AFC.
I agree with Trigonus in that it completely depends on what your growing.
As a rule of thumb, I would make the soil more organic for succulents and less for cacti. This is generally speaking though.
In terms of what to put in there, as far as cacti goes Trichocereus might be good because they are fairly tough for a lot of different conditions.
These are a column type of cactus that grow pretty fast and are easy to grow.
They are also more likely offset (branch) from the base being in the ground which would look beautiful in a few of years.
Just a suggestion.