1) If you're doubting your ability to always have time for a horse or are not ready for one, don't get one. Period. Like Spastic Dove suggested, try leasing a horse from the barn you're talking about. Most barns will have lesson horses for lease.
2) You don't necessarily need to go all-out and build a barn. Our horses are 24/7 pasture horses. They have a nice roomy (about 10X20 feet) 3-sided, covered shelter. Inside their shelter is their water tank and hay manger. We have 2 paddocks which can be seperated by a gate. The shelter can also be sectioned off into 2 stalls if need be (nasty weather, injury, etc.). This would eliminate the need to muck stalls regularily. We clean paddocks once a week.
3) Since you are unable to get a job, I'd say don't rely your parents for board money. Keep the horse at home and do the little bit of extra work. It takes 5 minutes to throw hay and feed grain. An hour a week to clean paddocks. It'll really save you (and your parents) a lot of money in the long run, and (I speak from experience) it is very rewarding to care for your own horse and you really create a strong bond that comes with being the horse's sole care-giver.
4) If you don't have the facilities for your horse at home, there's no need to rush into buying him. Buying a horse is a TON of responsibility. You can always make a downpayment or pay for him in full and bring him home when everything is ready for him.
Good luck with your first horse!
I bet you're super excited. I know I was. (And sorry for the novel. Lol)