Yeah, I work with some 3d modeling bits and know some modelers too and I can guarantee that this 6 month period probably is the whole process, photos, measurements, analysis, modelling, textures, rendering, optimizing... its a tough process. But I bet, they should have at least 30 modelers. If they started to model cars during the GT5 development (Kaz said they were still modelling stuff even after the game got released, and some stuff havent made it in time like the Scirocco)... They could have at least 20 fully modeled cars per month...
It's a crazy math, but I think you guys can understand...
Regarding new content, I think we're going to get between 30-40 new cars on spec2 (some cars that didnt make it in time, Scirocco, etc and some others that are nonsense to be missing, like the MKIV Supra), plus some standards converted to premium (the biggest part of Miatas, Skylines, etc, as its just a matter of adding badges and minor differences)...
Then they'll put like 50 cars as DLC to begin with. Plus, all that tracks that we discovered logos, mostly GT4 tracks with some minor rework.