Hello Norm,
I have been going to
LaManz for 5 or 6 years on vacation. There really is no need to rent a car. If you walk out the door of the Manzanillo airport there is a line of t@xis, and you can take one to LaManz.
You can taxi over to Tenacatita for the day. Take a bus to Melaque one morning. Everything in La Manz is walkable- lots of restaurants.
I hope this helps and you have a good visit. People are very friendly and you can ask lots of questions once you get there.