The rollfilm backs for the 2x3" Technikas attach differently from rollfilm backs for 4x5" Technikas. You want to be sure you have a groundglass back, at least one rollfilm back, and a viewfinder with a mask that corresponds to the format, if this is a model that doesn't have the top-mounted finder, and if it does have a top-mounted finder, you want to be sure you have all the masks you need for the lenses that are included and the format(s) you are shooting.
Super-Rollex backs have a lever wind, and old Rollex backs have a knob wind. The old ones will have frame spacing problems with certain films, due to the way they are designed. The Super-Rollex backs meter the actual film travel, and don't have this problem.
You also should have a grip--either the leather strap or the ergonomic grip.
The lenses should be serial number matched to the cam. A cam has three lobes and can support three lenses, usually in a combination like 65/100/180.
I like a Schneider 6x loupe on the 2x3" Tech. For larger cameras, I use a 4x or Toyo/Omega 3.3x long loupe.