The diving board area will be fine, but on your Arken the protrusion from the bottom of the scope will prevent your scope from sitting in the rings properly. You require a 1.5 inch mount for the Arken EP-5 to sit in the rings properly. I just bought one myself and found this out the hard way.
Yes, it should fit under the diving board. We generally recommend the 1.27" height unless you are mounting on an AR.
yes it will fit as long as you get the correct diameter
Yes, it should fit your 56mm objective lens size just fine. For most applications, our 1.27" height will be sufficient. If you need to clear a suppressor or a night-vision bridge, you might consider running the 1.5".