Sandblasting is better just much messier. Lots of yards won't let you do it but I guess you are home.
You can skip the Ospho if you do a good job sandblasting. Just get the paint on right away.
Re the epoxy comment on UV sensitivity it will chalk in direct sunlight. No probs on the keel but maybe on the hull below the waterline.
You probably don't want to spend big bucks so a household oil based outdoor primer and maybe top coat will do.
Yes, I am not at a marina. I have the boat at my auto repair shop.
Should I put the outdoor oil based primer and top coat on top of the barrier coat, or instead of the barrier coat?