In regards to the chattery motion you're talking about; make sure you've got the head on properly. The 190 legs have little screws that you need to tighten up into the notches in the base of the head (in my 501 at least, I'd assume it's similar for the 701) so that it locks in securely. I found this out once when I was swapping my head around between legs a bunch and forgot to tighten it down.
And in regards to the question about the 701/190 combo being able to support a jib, I'm skeptical. Even a 4' jib is going to put a bit of stress on the tripod and the 190 legs aren't exactly the beefiest things you'll encounter. If you do do it I'd reccomend only using the first stage of the tripod and weighing it down with sandbags or a heavy backpack. Overall I'm not too sure about that setup with a jib. But hey, it may work?