Kara is right, hoofs need to be done every 4-7 weeks depending on how fast the hoofs grow(my horses get done every 5 weeks). Teeth get checked twice a year(spring and fall).
Make sure you have the money to care for and have all of the necessities.
Make sure you have transportation to get to the barn acouple times a week and have the time to spend with the horse.
And NEVER be afraid to ask other experienced horse owners for help or to answer questions, I'm sure many are very willing to help you out.
If it's your first horse maybe try asking a trainer to come with to help pick out the horse as well and they can also answer more questions and give more details!
I'm willing to answer any questions you have about owning a horse if you have any!
I've always been told - the most important things are teeth and feet (no hoof no horse), teeth should be checked regularly, and that owning a horse can be the best thing to ever happen to you :)