You do have pretty good horses but they need to be fully blupped (100 blup) and then breed from your adult horses, that way you are breeding better quality foals that you can sell for better prices.

Hiya! I'm fairly new as well, but I'm currently working on breeding Mangalarga Marchador unis, so I figured I'd give my own input. Like @bronze1983 said, you do have some nice horses to work with, but you definitely need to BLUP them to get the most out of their offspring.

I personally pick my highest GP unis for priority breeding, and breed them at least once a day (sped up with aging points). For me, that's three birds with one stone: 1) BLUP them at a quicker rate, 2) get uni offspring faster, 3) age them faster so I can work towards my Yggdrasil milestones quicker. At the moment, my females are the highest priority. The males are the lowest because I can find higher GP, fully BLUPed in the public coverings. But once I start breeding male unis whose GP exceed the public covering ones, that's when I'll focus on them and use them for personal breeding.

In terms of goals, I'm not focusing too much on the selling aspect. I personally have not tried to sell any of my unis yet, but from what I've seen and heard from others, the overall values of unis are declining. Apparently it's pretty hard to sell one for even 10 passes. Again, that's just what I've heard/seen, so don't quote me on that lol. That being said, my current goal is to breed as high of a GP as possible and hopefully get them to rank high in competitions (Grand Prix and rosettes, primarily).

Maybe this is silly but to the both of you - what is BLUP & how do I improve it LOL

Howrse allows for a multitude of different playstyles and goals, and what you should do depends on what you want to do. Do you want to have the best GP horses? Do you just want to breed your own line of horses by yourself? Do you want to score high in the general rankings, be rich, or complete the trophies and/or collections? Do you want the extra challenge of doing non-inbred breeding, or breed crosses that dominate the breed rankings or competition rankings? All of these will require somewhat different approaches to gameplay.
If you're not sure, a good start is to try to work on the trophies, which will give you some prizes and even divine horses for completing a certain number.

One thing many players do is build up an AP farm to collect aging points to pursue their projects. This is just basically a bunch of horses, up to 1000, that you take care of everyday (no need for training), since each one has a chance of finding an AP when it wakes up.

BLUP is basically a measure of how well the horse is prepared to pass its genetic potential to its foals - positive means a larger increase in GP in the next generation and negative means less. To have 100 BLUP your horse needs 20 wins, to be 10 years old at least, and get all the skills it needs for the top 3 skills of the horse until the skills are bolded. There are BLUP schedule you can find for individual breeds in, for example, Dr. Zig's EC forum. For vanners, you'd train jump & dressage and do forest rides until no more skills, then do cross country comps until 20 wins, then train stamina and do mountain rides until no more skills.

Not silly at all, worry not! BLUPing is definitely confusing (took me a while to get a hang of it). First, you can take a look at your horse's BLUP status by going to their page and clicking their 'Genetic' tab. You should be able to see their Genetic Potential (GP) and under that is the BLUP bar. The goal is to get it from -100 to +100. In a nutshell, you want to fully train the horse's top 3 skills (varies depending on the breed), max out their forest and mountain rides, and enter competition to rack up 20 wins + additional skill points.

It takes a while to fully BLUP, especially since one of the requirements is for your horse to be at least 10 years old (though you can bypass that with certain black market items). Without items and the additional time set aside for breeding/missions, my horses typically fully BLUP out around 14 years old.

There's a very thorough guide on it which I don't have the link to, but perhaps another player might be able to share it

https://www.howrse.com/member/forum/topic/214950721-blup-and-training-discussion?page=0

BLUP guide is here. It's actually in this same forum, near the bottom of the page so no worries if you missed it.

And if you need blupping schedules here are the ones I have.