Straight onto your questions:
"Anyway I don't think pressing enter in a numeric text box should give me a warning."
Our developers will investigate the depicted behavior in a timely manner. Thank you for pointing out this issue - we updated your Telerik
"if a user leaves an input field blank/empty is there a way i can setup the input to default to 0 or something?"
Currently the "inputified" textbox doesn't accept zero as a value, but we will change this in the next release.
the Telerik team