110% Rule

Hello Everyone .
I am debating whether filing an alt 1 that falls under the 110 rule or take advantage of the full FAR that allows for a couple hundred more square feet. I understand if you fall outside the 110 percent rule it’s still an alt 1 but you must use the stricter code (same one as NB). I am going from 1 family to a 2 family with horizontal and vertical extensions.

question : what is the cost in complying with the newer code (and building more then 110%)? I was told SD1 and SD2 need to be filed but then I read on the DOB site that you no longer need to file for that . The main water line coming in is currently a 1 inch. The entire project FAR would be under 3,000 sq ft. Also Would the filing make a difference of whether I need sprinkler system or not? Any other helpful advice as to whether to stay under the 110% rule or not?

Notes: This is existing 2 story framed building (and yes i know all vertical extensions need to be non-combustible:).

Thanks in advance . It is very difficult getting accurate advice to this . I do appreciate it . Thanks.