once my Form1 goes through on my SBR with an 11.5 inch barrel and an overall length of 26 inches, i'm free to go ahead and put a collapsible stock on it (which then changes the over all length from 25.75 or so to closer to 30 inces), right?

i don't follow why they state a SBR is barrel less than 16 AND overall length less than 26, the overall length part seems to be unnecessary if the barrel length is the concern

First, yes you'll be fine.

Second, you misunderstand the definition of an SBR.  It's a rifle with a barrel less than 16" OR an overall length under 26".  

The "or" rather than "and" means only one of the two conditions needs to be met to consider it an SBR.  The overall purpose of including SBRs in the NFA was to tamp down "concealable" rifles people could carry around on their person, so having them be very short was the issue in the law.

You can in fact have a rifle where the barrel is 16" or longer, but it's still an SBR because the OAL is under 26".  Some bullpup designs could accomplish this.

For example: Swapping a thin buttplate on to a 16" Tavor.

thank you, I was going by this verbiage in an article
"a barrel under 16 inches and an overall length less than 26 inches, it now qualifies as an SBR."
sounds like it was a poorly written article