I do a lot of the 7mm Designer/European pens and although the tennon for the center band can be a pain, I think it is worth it. Start with the basic 24k or chrome kits and make sure you get your bushings from the same source as your kits! Not all the kits are the same. I had picked up some PSI bushings at a woodworking show and went to use them for my Berea kits and am glad I measured them first![:I]
As for turning, On The upper portion I usually follow the centerband size for about 3/4 of the length of the blank and then taper towards the end. I usually do not cut the tenon for the center band until I am close to the dementions I want to use. I use a centerband to gauge the where to start the tenon and start turning. I have found that if I use the bushings for my guage, the centerband will be too loose, so I will actually turn the tennon a little proud of the bushings and then use a real centerband to check for fit. Be careful not to cut the tenon too long or you may have to do an oops band:
On the lower portion of the blank I sometimes taper from the center to the nib, other times I keep the center diameter for most of the way and then taper to the nib. You will also find that the diameter of center end of the lower portion is not critical.
I think you will find these or the Cigar pens easier to turn than the slimlines. They are much more forgiving!
Good luck and Merry Christmas!