Didn't read all of it but the first and last page, skimmed the middle. For my lease we split the days (3 days for her, 4 days for me but he gets one day off of riding on my days) so we split all the monthly costs as well. We split farrier, board, feed, bedding, shots etc. so it comes to about $200 each. She just pays me her half and I cover paying all the different places/people and going out and getting supplies.
I pay for any necessary vet trips. She also has the option to show him, use of all my tack and I've offered her some of my days if she wants to come out more.
Unless you want to let her use more than 1/2 the days I think going halfsies on everything is a good idea. While I was skimming I saw you are thinking of asking for a leasing fee, what would that be for? From what I heard your horse is still green. Around here even for the most show broke horses, unless the actual barn is leasing them out, there is no 'leasing fee' just a break up of the costs of ownership. But maybe I mis-read.
Take a ride across the badlands
Feel that freedom on your face - Breathe in all that open space
You'll understand why God made -Those fly over states