Out of the engines you posted the Saito 100. It isn't going to hurt the plane and you will have A more usefull engine down the line. Magnums lack the power but not A real big deal, what they really lack is quality and they tend to wear out very fast. Ask yourself why they are only half the price of A name brand engine. The pumps on an OS are just that, A fuel pump. If you are going to spring for an OS the pumpers are always A good idea, you can mount your fuel tank anyplace in the plane without any fuel problems. Most people mount the fuel tanks right over the CG dead center.
I have A couple of all engines mentioned but my number one engines are the YS brand. Before you go to A four stroke you should check out what is the number one four stroke at your clubs, how many people do you know using them, it's A good idea to have someone close at hand to help you out with questions and to show you how to do things that is really using the same engine you buy.