You can tap as many phone as you want.  If you are tapping phones, and you have multiple engineers doing the TAP process, you will need to have enough CTI ports for the UCCX server to answer and supply the information to the phone.

For example, I usually only build out about 4 ports for Tapping.  For a typically small deployment of say 200 phones.   If Im tapping 1500 phones on a weekend, and I have 6 engineers (if you call them engineers for dialing a number, a joke).. then I will build out more ports for tapping.

When import the BAT sheet, you can import as many as you like.  CUCM does not really care how many its building.  Just that it does take time to build the device and if you 2000 devices in a BAT sheet, it could take a little time. (and replication, etc)