A drill and tap appropriate for the size nib housing you choose, a drill, tap and die appropriate for the size body and cap you decide on.
Expensive stuff like triple start tap an dies are really not needed to learn, and I personally don't like triple start threads for the cap much anyway.
Also a tap/die for the section to body threads (9 x .75 maybe or close to that) and maybe one for the finial threading if you make it small enough so that the section tap and die are too large (any size you want).
The nib housing thread you choose will dictate the tap and die you use for that, I use 11 and 12 mm (.75 pitch) for the cap threading, a 14 mm might be a better first choice as it gives you more "meat" to work with (I'm still in the learning phase and took a while to learn using the resulting thiner thickness of the smaller sizes, frustrating at best).
Pen parts would just be the clip and the nib/feed and housing, everything else is made in the process.