Agree with everything you said. I also think its easier to "ease" into the schedule. Keep a few hours of core sleep at night and still take your 30min naps every 4hrs until you feel like you're starting to get on the schedule. Then shrink and eventually eliminate the block of core sleep and you're there. Its never perfect, but at least it helps with the brutal agony of the adaptation period.

The biggest benefit of polyphasic is not squeezing every possible minute of awake time. Its the improved concentration and mood. If you want to leave 3-4hrs of core sleep at night thats perfectly fine.