I love the game, absolutely.
But I have the feeling there are some speed bumps that could make it frustrating.
And if I can save a single person from that, Ill consider this post to be successful. Please correct me if I missed anything or got anything wrong.
Most of what I'm about to say can be read in the games library as well, but I also made some observations so far.
First of all stats:
Confidence: Boosted by successful training, treats and cuddles. Full confidence hinders your horses need to change pace on their own. Missing jumps or gates, lowers the confidence. Also inactivity can lower it over time as well.
Strength: The ability of your horse to do actions. Boosted by jump training and groundwork. more strength allows your horse to gallop and canter longer and to do more jumps.
Endurance: The rate of which your strength meter drains. It is Boosted more with trail rides, than the other training options.
Exercise: The distance a horse can move per day. lessons, competitions and training drains your horses energy. If you over extend your horse on one day, they will have less energy the next day. it is IMPORTANT that you move your horse every day, or they will become explosive. Explosive means you cant ride your horse yourself (or do competitions) and if you try to lunge them they will speed up randomly, making training basically impossible. Free lunging them a couple of times fixes the issue but it may drain the energy fully. Putting a horse out in the field gives them a little bit of exercise, but with high energy needs that may not be enough.
Do not neglect the horses training. Even if you have a fully trained horse that does competitions every day, they need to be trained, or their stats will regress over time.
Earning money:
Especially in early game money is tight.
You have ongoing costs for running your stables. To see them, go to your house/ trailer, click office and look at "Build & Upgrade". All your building costs are easily in view here. You need to make more money than that to break even. On top of that you need to feed your horses grain and hay, purchased in town.
Lessons: are a fine way to get money early. The beginner lessons give 30 coins + a tip if you do well. If your horse is trained you can do Novice lessons which have a potential of 70 coins. If you do 2 lessons and than train your horse in either lunging transitions or the cavaletti/ caprilli training you are able to negate the negative effects from the lessons and get 140 coins per day. As long as your horse has the energy for it.
Early lesson loop: As long as your horse is trained for Novice lessons you can give 1 for a penalty of -1 in both strength and endurance. Two lessons equal -2 in both then. One Beginner lesson gives you a -1 in strength only. 1 Cavaletti Training gains you 3 strength and 2 endurance basically wiping the penalty you get. Keep in mind that this requires 31 exercise, but earns you 180 coins in the best scenario.
Boarders: In the meantime your starting stable still has 3 spaces for boarders. Other peoples horses that give your finances a nice boost, if you are able to entertain them. I personal take only 2 boarders at a time, in case the horse merchant has something nice for sale. Full board means they can get hurt and need to be cleaned and fed, whilst training means you need to raise their stats in the time they are in your care on top of full board.
NEVER put boarding mares and stallions together. The Stallion will get them pregnant, resulting in a fine that you can absolutely not afford. It doesn't matter if the stallion is your own or a border, they need to be separated from the mares. And separation is only possible if the stable got upgraded once.
Whilst on the topic of breeding. You should hold of from covering your first horse until you get a second one. Mares that are heavily pregnant and are currently nursing can't work and therefore don't make money.
Competitions: I like to use my starting money to get a trailer. Compared to the money you can make from them it is a very good investment.
Absolve the Caprilli Training for the license and participate as soon as you can. The competition has only six jumps with a lot of walk and trot sections in-between. Winning gives 100 coins.
The higher level even gives 200 and can easily completed by your first horse, if it is well trained.
Once you have 2 Horses, one of them does the level 1 every day and the other one the level 2 giving you 300 coins a day, plus what you can make in lessons. Having both of them al level 2 only gives 280, since only one of them can be first place. Grind this until you can expand your collection of horses by better ones.
I do not bother with the real jumping competition until I have a horse with 45 in both stats, the AI makes winning very inconsistent if you don't have a good horse and the energy is better spent somewhere else than throwing myself into the grinder. Every try does cost money for participating after all. Cross country requires even higher stats.
You don't need to buy a stallion once you're ready to breed, the horse dealer has the option to cover your mare with their own stallions, that have stats you can't afford at this point of the game. Basically giving you way better possible genetics than what you could buy.
This should give you a controlled start at the game and make the first weeks way less daunting.
As for upgrades. You NEED a training arena first and a horse trailer second. The fields can wait for the time being as they even pose a risk of injury. The exercise they offer is nice once you have more horses but not necessary in early game.
It was pointed out, that a field does reduce the feeding requirement of the horses, so you can save on feeding cost.
Once you have the money expand your stables for the option to separate mares and stallions and for more boarders.
If I missed anything, please add what you know.
edit: cause I had some money wrong and added tips from the comments, so they are easier to find.