Its 200 per item. One for the SBR LOWER, one for the supressor.
If the lower wasn't registered as a pistol or Sbr, its not legal to build into an SBR doing the traditional tax stamp process.
Once it is (or assuming this one is) registered, you can then put any upper you want on it, from 4" to 24".
Lately, it is a 6-12 month waiting period.
While you are waiting for each tax stamp, its illegal to own the firearm, or suppressor or have it in your possession. C III xfers are best handled through an intermediary FFL holder who will hold onto the rifle while you are waiting tax stamps.