Well it all depends on what you want to do in the ESRPG. Do you plan on just entering discipline shows?
If so, all you need are competitors.
If you plan on breeding and entering breed shows, you will also need breeders.
All stables (if you plan on housing your horses and characters in your own stable) will be required to have staff members (but you can hire those, if you don't want to play them yourself.)
So those 3 careers are the most important. The others are more like services to others (though they can also serve you. IE if you don't want to have to wait for someone to host clinics to gain XP for your athletes and competitors, you may want to have a trainer and instructor of your own as well. Same with shows. You only need a show manager if you plan on hosting shows.
One thing to keep in mind, is that each character can have 2 careers. This means that your competitor may also be a breeder.
Another thing to remember is you only need so many competitors/breeders for shows. It all depends on how many horses you plan on entering in shows at a time. Competitors and Breeders can enter 1 horse per show up to level 4, after that they can enter 2 horses per show up to level 8. At level 8 and beyond they can enter 3 horses per show. So if you plan on entering only 2-3 horses you may not want to have more than 2 breeders/competitors (unless you are doing a lot of diverse disciplines.)
Here is an example on what characters you would need for a small breeding/competing stable specialized in both western and saddle seat (10 horses):
- barn manager / competitor (western)
- stable hand / breeder
- competitor (saddle seat) / breeder
- competitor (western) / competitor (saddle seat)
With these 4 characters, you can enter 2 horses in breed shows at the beginning of everybody's career, 2 in saddle seat shows and 2 in western shows. By the end of everybody's career, you'll be able to enter 6 in breed shows, and 6 in each discipline. Moreover nothing prevents you from assigning more than 3 horses to a competitor/breeder. The restriction is only on the amount of horses entered in 1 show. Competitor A could enter horse 1, 2, and 3 one show and horses 2, 3 and 4 next show.
I think most people running a full fledged stable will have more than 4 characters anyway, so I wouldn't worry too much about needing too many.
I am actually not sure on this. I think we will be using the same ones and just have some additional directories, but @christinahanson would be able to give a better answer than me on this one.
Let me know if you have any more questions