I agree with the others. you would be better off getting a trainer first. Once you've mastered that, you can move to a mid wing or low wing trainer. Not all mid wing planes are created equal, so without knowing about the plane in question it's kind of hard to answer whether you could learn on it. Since you will be new to planes, it's also hard for you to evaluate how well the plane was built, what condition it's in, what kind of flying characteristics it has, etc. Unless you have some way to assess these things, you might want to pass on it. Of course since it's owned by your father's friend, you should be able to trust him more than a stranger. If he knows it's easy to fly, has seen how you do with boats, and is going to help you learn, perhaps you could learn with it. I had boat and car experience before I learned to fly. I can say it definitely helped, but flying was definitely harder. The biggest difference is the plane has to come down. Developing the skills to keep it in one piece takes time.

On to the recommended trainer planes. There is no "best" trainer. I do NOT recommend RTF or package deals. These package deals are good if you don't want to invest the time researching and selecting components yourself. Every time I've run the numbers it's been obvious you can do as well or better selecting the individual components yourself. Most of the ARF trainers from a known name will do fine. Since trainers are somewhat disposable, you buy them to learn, and then move on to "nicer" planes, I usually recommend looking at the less expensive end of the scale. The Nexstar certainly is nice, but many people find it's got many bells and whistles that are not necessary for learning. One of the lowest priced trainers is the Tower Trainer. Obviously, you will need an engine and radio. If you do decide to get the plane from your dad's friend, pick an engine for you trainer that will go well in the mid wing. Then you can move the engine when you are finished training. Your choice of radio depends on your budget. If your funds are very limited, go for a basic 4 channel like the Futaba 4YF or an equivalent from JR or even Hitec. If you've got a little extra to spend, look at the basic 6 channel computer radios like the Futaba 6EXA. They have many features that you can use as a beginner, and will get you through several planes, or even for years. If you do go the 4 channel route, make sure it comes with a 6 or 7 channel receiver. This way it will give you full function if you later decide to upgrade to a computer radio.

Good luck