FYI, I am pretty sure the direct lift comes with casters and drip trays.. You will need a fork lift to get it off the truck. Many truck drivers won't wait for you off load it piece by piece. The other option is to pick it up at the freight dock and have them put it on your own trailer with...
The benefits of a two post are obvious. Just make sure your builder has a clear blue print of the tension cables. Also I would ask him if he would be liable? Just to cover your a** a little bit.
Derek is a great company and sells a great lift. Direct lifts are owned by Rotary (FYI) there is much of any margin in these lifts. I wouldn't hold your breath. FYI, Rotary sets up territories so Derek isn't supposed to ship outside his territory. Freight on a 1600lbs lift is crazy.
Just my 2 cents. Be very careful with PT. You cut one and everything gets really ugly very fast! I have been selling and installing lifts for 20+years. I won't install a lift on a floor with PT or in floor heat. Question is why can't you do a four post that doesn't require drilling?