+1 on the drive pins, started with the three most common but found out quickly there are more shafts out there with "uncommon" threads than I imagined.
Also, get a good collection of collets, ferrule, butt, and joint sized, in a pinch you can make a joint collet work for shaft cleaning if you don't have the correct pin.
Get a good stock of tips. Most of my clients have been going to Ultraskins so I try to have at least 4 or 5 of each of them in stock plus a box of Triangles, Le Pros, and Elk Masters. That will give you a good start. If someone is dead set on a Kamui or Moori or something like that they can supply or I'll order for an additional fee. Stocking them is too expensive for my volume.
As far a a tip shaper goes.... I thought I was going to order one as it seemed like a pretty slick way to shape tips but found myself adopting the method of installation shown in the video below and it works perfect for me so I'll stick with it.
https://www.youtube.com/watch?time_continue=4&v=ElB9LhdjX8A
Chris Hightower has a tip shaping fixture on his site for nickel, dime, and penny radii similar to the one in the video. It's a nice way to go and gives you a little more flexability.
Sharp blades are a must. I buy in packs of 50 or 100. For trimming the tip sides I do it as shown in the video and only use one section of blade for each tip. For shaping I usually go two tips per blade. Then they get turned into box cutters.
Get yourself some ferrule material and some cheap dowels (or old shafts) and practice ferrules. It won't be long before you discover a cracked ferrule while doing a tip replacement and you'll want to be able to take it in stride.
Other items to put on your wish list:
Drill chuck and common bits for your tailstock (for ferrules and later joints)
mini boring bar (comes in handy for all kinds of things)
not necessary but really nice to have.... tip centering tool (or you can get by with a concave live center)
I'm by no means an expert, but this has been my experience. Hope it helps.