I'll tell you how I show. I've always been showing the same way. I don't know if it's the most effective way, but it does earn me money instead of losing it.
I only have AD (all disciplines) horses. I show geldings, mares, stallions, everything that moves really. :) I try to make sure their riders are always at their or a higher level, but it doesn't always work out. Try to make sure every rider has always at least 5 horses assigned to them, it's not worth the money to pay a rider to only ride 1 horse.
Now to the showing itself. I show based on the training bars (str, mv, spd, etc.). Every showing discipline works with 3 of those bars (dressage - str, mv, int; xc - str, spd, hrt; jumping - spd, scp, hrt). So when you want to show a horse in dressage, you only need to look at str, mv, int, and can disregard all the other bars for the moment.
So after training each week, I go through my barns and look at the horses' bars. I only show the horses who have at least twice as many bars in all the traits of a discipline as is their current level and more than that in at least one of the traits. What I mean by that:
Take a yearling that's on level 1 in all the disciplines. I won't show the yearling until it has at least 2 bars in 2 of the relevant stats, and 3 in the third one. So if I were to show it e. g. in jumping, I'd wait until the yearling was up 2 bars in e. g. hrt and scp, and up 3 bars in spd.
The same goes for all the other levels as well. E. g. on the level 6, I'd require the horse to have 2 stats with 12 bars, and a stat with 13 before showing them.
Important! Doing this doesn't mean the horses will always place well. They can sometimes be lined up against stronger horses and lose. If your horse ends up 7th or worse in a show (i. e. starts losing money), always look at their score (e. g. % in dressage). If they haver 75+% in dressage, <10.00 in xc and <12 faults in jumping, I keep showing the horse even if they ended up last.
Important! All horses are different. Sometimes they're ready to show earlier (e. g. a 6th level horse can do remarkably well with 3x12 stats instead of 2x12+1x13).
Important! Sometimes a horse is very weak in a trait, e. g. int (
https://horseeden.com/horse.php?id=20223992 ). In that case don't wait until they reach the required nr of bars in said trait and instead try to balance it with the other 2. E. g. for a level 4 horse it could be this: 10 bars in strength, 10 bars in movement, 6 bars in intelligence.
Important! When you're unsure (the bars look promising but there's room for doubt), consult the horse's showing history. With some experience you'll be able to estimate the horse's readiness to show from the last time you showed them and the score they had.
Hope I wasn't too confusing. If you have further questions, shoot me a pm. :D