Just about any servo with a J style connector will work. S Bus really isn’t worth mentioning as it’s mainly used when running multiple servos on a single function. Think 3 or 4 servos on a single aileron. It helps to get the servos synced and reduces the amount of wiring used. You can use digital servos as well as programmable servos, just won’t get full potential out of them. For most sport flying a typical 50oz output analog servo will work just fine. After replacing your batteries I see no reason why you can’t use what you have. In fact if you are interested in an additional FM receiver I have one I would be happy to send you.