Hi Dave,
I do analog summing, in my case I have a 16 channel SSL with their stereo bus compressor and stereo EQ and a bunch of other outboard processors.
re: your questions:
1. I don't think there is a best practice for this, other than "until it sounds the way you want". Keep in mind that you're adding distortion with every pass, so at some point it's gonna make things sound bad, but other than that it's a purely subjective thing. Also, if you've got anything resembling decent converters the amount of distortion you're adding with just conversion passes is pretty minimal, so I wouldn't worry to much about it unless you're doing lots of passes. Again, let your ears be your guide, but don't worry about it too much. Lots of folks still use outboard all the time, and if conversion passes were really messing up your sound that much no one would still be buying 1176's and Distressors.
2. I don't think so, at least not until it sounds bad.
3. Yep, my "print" track is fairly hot, but leave some room for the M.E./Film Editor/whatever if you're sending it out to anyone else. I try not to peak much higher than -6dbfs. Remember that if you're looking for saturation in your console you should be able to saturate your console channels and the internal mix bus and then theoretically turn down your master output to print at reasonable levels back into Sonar.
4. I don't use console emulators much. Sometimes I'll drop one on a track because I want to soften it a bit in a specific way, but it's not super common. Keep in mind that you should really mix through your console so you can account for its sound while you're mixing. If you're doing that then you essentially have a "console emulator" on each track anyway, only it's not an emulator at all, it's the actual console. If you want to do something in addition and the console emulator lets you do that, IMHO do what sounds good.
As far as my method goes, I route all tracks to more-or-less standard stems (drums, bass git, vox, bgv, fx, and what have you) and then send those out hardware outputs to my SSL. The SSL then sums and sends everything through the bus comp and stereo EQ and whatever other outboard I happen to be using on that mix. From there the SSL has its main out coming into my "print" track which is going to the Master bus in Sonar ("print" tracks are the ONLY things feeding the Master bus in this scenario). I enable live monitoring on my print track so that I'm listening to the signal coming into that track when I mix. The Master bus then has analyzers, A/B tools, metering and ARC?whatever on it so I can do measurements and comparisons. When I'm ready to print I record arm the print track, name it something like "OMG NEXT GIANT POP HIT 9-22-15 A" and hit record. If I make adjustments I create a new print track, change the track title to reflect current date, revision letter and, if necessary, usage ("OMG NEXT GIANT POP HIT 9-22-15 B, TV mix") and record again. This way each of my mix revisions occupies a separate track and I can A/B them or export them individually.
Dean