Hmm, 91 size 4c fuel injected engine

If the 4star did not come with a mount, you can try a GP mount 46-60 size. It will fit even though it is advertised as undersized.

For the prop, download / obtain the manual from the web if you dont have one and go for the recommended prop. I think a 14x6 would be good. If you are learning the hobby, go with Master Airscrew so you dont break it if you have a ground strike. There is a prop table somewhwre in RCU if you search for something like "which prop"

Ameyam