RE: How much work is too much on an ARF?
The simple answer to the OP's question is however much you, keyword here is you, willing to do or want to do. This hobby is about what the individual want's irregardless of other's. I personally don't care what someone else buy's, build's, assemble's. etc. etc. etc.
I like all version's at different point's in time. If I don't want to build it then it's an arf. An example is, I really have been wanting a pitts. RCGuys has one but I have the time, and desire, so I will build it from plans. My Ultimate is an ARF from Great Planes. I wanted one and did not have the desire to buld it. So! It really is just a matter of what you, the individual, wants. Nothing more nothing less.
Enjoy whichever aspect you desire.