Gosh I want to type something, but everytime I start, I get so frustrated I just can't finish my thoughts.
Just to breed your mare because she's super nice, personality wise (at least this is what I got pretty much from your last post) is no reason to breed. Even if the stud fee is only $500 you are going to spend at least $2500 to $3000, before that foal even hits the ground.
Your mare needs to be seen by a vet to make sure she can carry the foal, ultra sound and biopsy. Then you have to decide whether you are going to do live cover or AI. If it's live cover and your mare has never been bred and she is older, the stallion owner (if they are worth their salt) may wish to sedate your mare, so their stallion does not get injured during this process. Also you will need to take the mare to the stallion (fuel costs) and pay for mare care ($10 a day more or less). Your mare could be there as long as 30 days or more, depending on her cycling.
If you are going to do AI, then you have to order the semen, pay for the product, pay for shipping + deposit on container (and read the fine print about if it is damaged), you have to have your mare given a shot to bring her into season and then you have to have the vet or stallion owner administer the AI.
Then at 16 days you have to have your mare ultrasounded to make sure that she took, if she didn't then repeat steps 1 & 2. If she did take then you should have another ultrasound at 90 days to make sure she didn't sluff the foal. If she sluffed the foal repeat steps 1 & 2 unless it is too late in the breeding season and then you have to wait until next spring.
Also, keep in mind. Some stallion owners only stand there stallions during a certain part of the year, March thru July for expample.
I bred my TB mare for a foal that I intend to keep until death do us part and I could have purchased at least 4 yearlings for what I paid in prenatal care, before he even hit the ground. I knew this going in, so no surprise.
You then have to give your mare 3 neumabort shots during the course of the pregnancy to make sure she does not abort the foal. If all goes well and your mare foals, then you've got 3 yrs. of feeding and vetting your offspring, before you can really start riding your byproduct of this breeding. So, really think about it.
She is a nice looking horse, but I'm sure you and your family could find a nice replacement for a reasonable sum, without having to put this nice mare through the breeding/foaling process, just for a nice, good minded riding horse (nothing wrong with a nice riding horse, don't jump on me, they are worth their weight in gold).