One very important question to answer is about the horse you are thinking about leasing?
Since it's been a while since you rode and you're probably a bit rusty and not overly confident, be sure that if you lease a horse, it is a good school master for you, someone who is quiet and who can forgive your inevitable learning curve mistakes. Don't lease a horse who is going to be a disaster waiting to happen. I would also make sure you are working with a knowledgeable instructor who can make sure you are learning to ride properly and not developing bad habits.
Take it slow and be sensible!