First of all, I'm very impressed by the action you are taking. You are being very mature about the situation, making a list and being realistic about costs. Second, if you are just looking for a pleasure horse, I would recommend a Western saddle. I find them more comfortable, and I definitely feel more secure in them. Not to mention the saddle horn is great for holding bags, so if you go on trail rides you can have lunch and a water bottle sitting right in front of you.
About leasing or buying, see if you can talk to the stable about leasing to buy. It's a deal where you lease the horse for whatever amount per month. If you decide you want to buy him or her, the cost you have spent leasing the horse will go towards the cost of the horse (that will have been agreed upon prior to the leasing). If you lease the horse long enough to pay it off before deciding to buy, then the extra money could go towards boarding costs. So for example, if you decide that the horse will cost $3,000 total, and you lease for three months at $150 per month before deciding to buy, that $450 you have spent leasing the horse would be deducted from the final cost of the horse. It's an option to consider, anyways :)