...I love my gelding and can't imagine life without him. But you have to be really, really dedicated to keeping a horse in order to make the money and time and effort worth it.
Ditto to everything Sheilah said (except, Sheilah, you can learn to clean a gelding or stallion's sheath, and give injections too, lol).
It IS really important to find out what training they have had, how long ago, have they been worked recently, how they are as far as handling, grooming, etc. In other words, temperament is even more important with a beginner's horse than it is for a beginner's GSD. How old are they? For a beginner, horses over 10 years old would be a big advantage. No stallions--mares or geldings only! What breed are they? That can make a big difference also. Are you in an area where they would have to have shelter or be stabled for the winter? Winter time brings its own difficulties, my favorite was making sure 3 times a day that they had water they could drink, not ice, in single digit temperatures.
If they would be stabled, they need their stalls cleaned daily, their feet cleaned out daily, grooming is an essential for a healthy coat.
And as everyone else stated, they are VERY costly to keep the way horses should be kept.
I trained and showed for most of my adult life, as well as giving riding lessons. The 2 breeds I worked with predominately were Arabians and Thoroughbreds, Arabs being the breed with the most intelligence and stability, TBs also with lots of intelligence, but often unpredictable, depending on early training. I always 'trained,' never 'broke' a horse. Still, now in my sixties, I deal with lots of arthritis and a damaged back, not just from equestrian accidents, but also just the heavy work involved (unless you are wealthy and have someone else to do that for you).
I nearly forgot to re-emphasize what others have stated--if there is a way for a horse to injure himself, he will find it! I knew a veterinarian who owned horses, he had cut down young trees in a pasture and left the trunks about 4 ft. high (he was afraid the horses would get hurt if he cut them lower, and couldn't take them out by the roots right away). You guessed it--one of his horses impaled himself on a tree trunk, right through the chest!
I dearly loved horses all my life (still do), and I don't want to discourage you, but I would want you to walk into a commitment like this with your eyes wide open! It really would be the best if you could work under an experienced, knowledgeable horse owner, a mentor, before you take this on.