this is by jvroig it should help
In my opinion only, do the isolation movements during the start of your cycle because this is when your compound movements are lighter - perhaps certain participating muscle groups like biceps and triceps could use more recruitment, so why not add them now? By the time you go to the 5's, hey, the biceps and triceps will be exposed to greater load in the compounds, so we might not need them there.
But don't start them off using light loads. Although you start them early in the cycle, use a heavy load. I can't say how much, this isn't a strict rule. I'd say do something like your 10RM, or maybe heavier.
As for the stretch, a good idea (and again just my opinion), since you start heavy on the isolation while your compounds are still light (to increase recruitment) would be to choose an isolation with regular stretch only (again, since the compounds aren't heavy yet but we start the iso heavy), then when you max out the iso exercise, you'll probably be jsut starting out with your heavy compounds. When that happens, instead of stopping your isolation exercise, you can still do a little of it, this time using a different exercise that has significantly more stretch. For example, you start heavy on regular curls. When you max out on this, it's already getting really heavy on your compounds anyway, so you drop this particular exercise and instead do an incline dumbbell curl - although you'll be dealing with less weight (since you already maxed out on your curl), you'll be getting more stretch, which is exactly what you need now since the compounds will probably overload your arms already anyway now that these compounds are heavy already