Ok so shows that follow the ESRPG template, can be made "ESRPG affiliated" by the host. If the show is ESRPG affiliated, you have potential to earn more ESRPG XP points.
Anyone can earn ESRPG XP as soon as they register their horses and characters (see the ESRPG section of the forum), and anyone can host ESRPG affiliated shows. You do not have to be staff or have been on this forum for a specific amount of time.
The only things you need are for the show to be about a discipline (or a breed show), to follow (more or less) the template provided in the competition board, and to produce winners.
In fact we recommend for shows that follow those guidelines to be affiliated as they will likely get more entries than unaffiliated shows.
Affiliated shows do not have to be the regular boring discipline shows we all know very well. You can have themes within them (like say 'costumes' or 'must wear a specific color' etc) and even challenges (like 'must use a specific angle' or 'must use a specific pose' or even 'portray a specific scenario').
Creativity is close to endless in that regard.
If the event you want to host doesn't produce winners, then it would be a workshop.
When we started this forum, ESRPG was just a small thing we put in here, but as we are developing it, it should take over all of this forum. (we'll probably do away with the achievement section and the legacy section...)
Oh and clarification on the whole Equus Sims vs. Equus Community thing: neither site is affiliated to one another anymore and hasn't been since the creation of this forum over a year ago. What they do on EC has 0 impact or relevance on this forum and vice versa.
At this point in time, ES and EC are completely separate sites with no ties whatsoever. You are welcome to play your horses on both (and other sites like Russian ES and more) sites however, but know whatever achievements you may gain on those other sites, will have zero impact on this site. Hope that helps!