I'd suggest "use your ears" stereotype comment, but that's annoying
On the other hand, gain staging is important, not just for "analog modeled" plugs, but for most
What helped me the most is that utility called "plugin analyzer" which kinda gives you precise info what each plug is doing - THD, phase shifting, etc
To me, that was a big help with demystifying plugins
None of available plugs is the exact copy of its analog counterparts, which is normal, but you get the info which part of analog modeling they focused on and eventually got it pretty good. Most of "analog" plugs just emulate harmonic distortion
To answer your question - I think it's better to keep levels not higher than -6db's
That helps not to overload plugs with distortion they produce and believe me it's easier to drive plugs harder than you actually want and hear.