Our indoor, if yours is outside that may make a difference, is 120’ x 250’, 20’ on one end roping boxes, so 230’ riding area.
Has been used mostly for young ranch horses, roping, reining and working cow horse, along with some 4H and Little Britches all around training.
Base was wetted and compacted with pure topsoil and footing itself triple washed finer sand.
That sand would be too fine for outdoors, it would blow away in our windy country.
We train many young horses, footing needs to be shallow so they don’t have to dig thru heavy material and so chance soft tissue injuries and deep enough so when they go faster they don’t fly and scare themselves or slip trying to turn/stop.
We try to maintain a 3 1/2" depth at most. We use a tape marked yard stick to measure depth regularly.
More important for us is to keep the ground worked often so it is flat and even all over.
Best I remember, initially we had 12 big belly dumps delivering the sand, that was leveled with laser on a grader and then they added another 3/4 trucks.
Over the years we had to add about 4 trucks twice and has worked wonderfully.
Never had any injuries we know of from the footing, horses and trainers really love it.
4H older kid’s horses especially appreciate a footing kind to their aging bodies, we think.
We keep it watered regularly to control dust, but a bit on the dry, lighter side.
For roping training, using a dragging roping dummy has been a game changer.
So much can be taught slow and easy until the basics are firm on hand.
I think it would be fine as is for jumping training also, especially cavalletti, gymnastic work and lower height courses.
For more advanced, faster work in any discipline, with bigger efforts expected, we would try to keep it a bit more moist, so to have some more grip, expecting only fit, more experienced horses to be using it then.
We could also work it up a bit drier and so faster, that would be closer to competition conditions, but would not want the young inexperienced ones to scare themselves before being ready by going too fast to have good control.
We have an outside arena for horses to experience working on different footing also.
Indoors is mostly for more precise and all weather training.
Don’t know if any of this applies to your situation, but maybe it will help you if some may.
Taking care of footing is an ongoing learning experience and each arena has its own quirks.
Horses will let you know by how they respond if they are unconcerned or worried working on whatever footing you provide, listen to them. 
) and get them out for a quote on what they think we need to do. I should have just called them in the first place.