Bruce,
I have smoked with no pan, but have always used Kingsford. I have lump on the patio, and use it for grilling on my WSM, but as you know it burns hotter than Kingsford and would require close monitoring. You could limit the amount of lump in the chamber and not use the pan - but I would not fill the entire chamber with lump - then keep the vents nearly completely closed. This however seems like too much work to me. I've said before, I like to sleep during overnight butt smokes and I would not chose a method that requires close monitoring. Thats just me.
You could use Kinsford with a few pieces of lump (I would still use my standard two pieces of fist sized oak though). I recommend not filling the charcoal chamber completely with lump with the water pan removed. You can always add Kingsford, lump or wood chunks later in the smoke, depending on the temp of the smoker. If your WSM gets too hot, it can be tricky to lower the temp. But you probably knew that already.
Hope this helps.
Glenn