If I were you I would get the mandrel, barrel cleaner set, a 7 mm drill bit, and if you have a vise you can use it as a pen press. You will also need a DP vise or something to use as a centering jig to drill your holes. If not they sell pre-drilled blanks at PSI. I use a carbide scraper for all my pens but you can use a regular scraper or other tools if your comfortable with them. You will also need CA glue a nail punch or something similar and your choice of finishes. I use CA, Canuba wax stick and a polishing compound but that up to you.
I get almost everything from PSI except the barrel cleaner I ordered mine from craft supply or Rockler. PSI has a 8 pen sampler set of the 7 mm pens
that is like $34 and it comes with the bushings I believe.
is to cut the blanks to the proper length 2 1/16 for most 7 mm pens. (if your blank is 5-6 inches before you cut it use a pen or marker to draw a line on one side long ways but don't go all the way to the ends.) This will work as registration mark for the grain when you put it on the mandrel.
drill your holes using a centering jig or vise.
is rough up the brass tubes bith sandpaper and apply aome CA glue, enough to hold but not have it spilling out the other end. Then using a punch insert the tubes into the blanks with a twist while insuring they are seated correctly.
During this step if you have multiple blans of the same species draw a number one on each side of the line you have drawn. Then a 2 and so one. This way you know which 2 pieces go together and how they were originally oriented before cut in half.
After the tubes are glued and dried using you barrel cleaner in the drill press and you blank in the centering jig/vise, run the barrel cleaner in the tube. This does two things it gets any glue out the tube and as you apply pressure it also cuts and flattens the ends of the blanks. do this to both sides of the blanks until you see the edge of the brass tubes.
assuming your mandrel is in the lathe already you will put the proper bushing on then one 1/2 of the pen blank another bushing and then the other 1/2 followed by another bushing. Tighten it all up on the mandrel the bring your tail stock up to the end of the mandrel. Snug it up and when you start the lathe (I use high for the entire process) you should here that little hum.
using your choice of tools shape your pen. You have turned other things so no need to say all that stuff. You want to go up to the bushing without cutting into it and leaving enough room for sanding to the thickness of the bushing. You don't want to got below the bushing slightly thicker is better.
I sand from 150 - 1000 on most pens then up to 4000 after the finish has been applied.
My finish for wood is using a paper towel square about 4 layers thick (bounty to be specific) to apply the CA while it is spinning then I spray some accelerator. 3-4 coats min then I buff that with 1000 - 4000 grit. I then apply canuba wax buff with a soft cloth then use a polishing compound to finish. all while spinning on high. The polishing compound has to heat up a little so apply a little pinching pressure until it does. Not to much
is to assemble your pen I use a pen vise but did use a regular vise with wood pads and some use a table and rubber mallet.
I hope this helps and make sense.