I wouldn't use threaded rod for anchor bolts. At least make them out of 4140, and only thread the necessary part.
Yeah, there is a bit of math involved for cantilever designs. Really cool, but probably not the best option in a DIY situation if safety is a concern. You'll need a robust anchoring system, which will probably require a lot of concrete. You live in NY, so you have to consider heavy wet snow loads, so yeah, there is a bunch to deal with.
For reference, I just shot off an RFQ for (2) 12@31.8 x 40' American Standard I beams to one of our steel suppliers. This will be the highest priced supplier. I'll let you know what they say tomorrow.
