From my experience, halter's a really great option for 5-3 starred horses, no matter the PS. This also gives them the best chance at acquiring levels the fastest. My 2-1 starred ones however perform pretty badly more often than not, so I tend to keep them in discipline shows. In terms of showing horses in general, most of mine do fairly well, including foundies, who are still bringing home about $3 in profit from each show even when they place low.

If you are worried financially, I would throw any horses that don't have the BS for halters and the lack of performance for discipline shows into careers. They will still gain experience for skills this way and always bring home money. You could put them through careers for a couple in-game years then test them in their discipline shows again to see if they've improved.

When they get entered into halter shows exclusively can you still train them in their disciplines to boost PS for breeding purposes?

yes, as long as a horse has a discipline set it can be trained regardless of what working paths they're set to

Okay, most of my horses are 4-5 stars so any of them would be suitable for it or should it be the ones that have more excellents have a higher chance of winning?

and from my understanding halter is a faster was of leveling up a horse?

Yep! Halter shows give a notably larger amount of xp than discipline shows.

Does halter earn more money then too?Cause I remember back in the old days when there would be 200-300 horses in a single show and now it seems like the majority of the discipline shows have no entires except for my horses

I'd like to add that at some point halter shows do not become the best to show in. Halter show points do cap out. It's somewhere around State Tier 2 where you'll want to switch to Discipline as you'll start to get more points than in Halter. Sometimes if you're on the cusp of changing from a show level you can also end up getting more in discipline points than in halter points. Honestly I just watch my horses points and I'll show them in both or I'll "test" discipline shows, by showing them one day in discipline shows and then I compare their stats to how they did in halter. If their points they're earning in Disc are half or more than the points they earn in Halter (because halter takes 20 energy and disc is 10 energy) then they get switched to disc. Example If they're earning 900 points in 1 halter show and 600  points in a discipline show, I switch them to Discipline because Disc takes half the energy and 600 x 2 = 1200 so they are earning more points in disc. 

@Equire - to answer your question halter shows only can have 20 horses and then they run. Disc shows are unlimited by they run 4 times a day now. (every 6 hours). As for which earns you more money it really depends on how well your horses are placing. I've found low placers in halter will lose money but they still get more points then in disc so I just keep them in halter. 

Is there a more efficient way to check the points they earn? Having to go through and individually check over 500 horses seems like a bit of a pain haha on that note as well what's the most time efficent way to show so many horses? Cause when I go to the show arena I have to click on every show anyways to use the enter all button and it ends up still taking me almost 2 hours a night 😅

Unfortunately there is not really an efficient way to check the point they earn other than just by going to their page and looking at the history. I have a spreadsheet that I made that calculates what percentile they are in for their show level so that horses that are on the cusp or towards the end of it are highlighted so I can go check them specifically. However my husband helped me make it and I was working on finding a way to get it into google sheets and I just haven't had the time to dig into it more. 

The other method I do is just go to the performance tab in Herd Management and looks for all State Tier 2s and check them. Or if you use alfs spreadsheet for charting your horses (its linked in the Discord) you could potentially use that and then just put in the horse id into the horse page url and go that route as well. 

As for the most efficient way to show there really isn't a good one if you've got all the enter alls. Personally I find showing a couple times during the day the best. I usually halter all my horses first (any dis horses have halter unchecked in their paths) and I use EA2 for that. Then I try to disc show half my horses before one of the show rollovers during the day. I use EA1 because theoretically you want them more spread out instead of all in one shows so you win more points. Then I try to EA1 the last half of my shows before energy rollover. 

but lets face it, sometimes I don't do all that and I'm in a rush and just EA2 everything halter and disc.