If you want to use rigid tapping then yes, you need spindle control.2. How will sheetcam reverse my spindle? Do I need spindle control?
There are three ways of doing this.3. Do I need a special tapping holder (compression/ extention)
1 Solid tap holder or collet chuck. The tap is rigidly held and you need very accurate spindle/feed synchronization. This is not really a practical solution for an X3 retrofit.
2) Rigid tapping head. These have some Z travel and are spring loaded. With care and some experimentation you should be able to get one of these to work. You do need fairly accurate synchronization between the spindle and feed.
3) Automatic tapping head (aka tapmatic). These have built in clutches and a gearbox. The spindle keeps running in the same direction. When you stop feeding down the tap stops rotating. When you feed up, the head automatically reverses. These heads are the easiest to use but they are quite long so you need a fair amount of Z travel.
Go to the Tapmatic website and have a look at their technical information. There is a lot of useful information in there.