''The hardest one for me is when the weather reports cumulus and some you can see in the afternoon starts to build, and one or more occasional showers. But no reported CBs yet. Do you go imc in that weather?''
Probably, but depends on the route, availability of alternates, availability of regular weather updates, terrain, duration of planned flight, equipment, endurance, experience level, etc, etc. But there's a lot you can do. Select a level that puts you in VMC whilst on an IFR flight-plan, so that you can avoid visually if necessary. Get reports from aircraft ahead. Get reports from ground stations ahead. Ask for avoidance around build-up. Enter a hold and wait it out, the fireworks can be over quickly, or it may move along with the wind. A quick diversion to wait for 30 minutes before resuming your trip is no big deal, as is a smart 180-degree-turn, and so on. But in the end, if I ascertained that there was any chance whatsoever of accidentally penetrating a CB (the real deal, not the fluffy little Cu that's a bit moist and choppy, you know what I mean), I wouldn't go.
''If there is isolated CBs do you go imc and then around the CBs if you see them?''
No, if I did not have the means to avoid the CBs (i.e., radar) I would not go IMC, too great a chance of accidentally penetrating one.
''I guess embedded CBs you avoid and go visual?''
If there were embedded CBs and I had no way of detecting them if in IMC, I would definately remain VFR.