No, the code allows a 2" vent. You can use a 3" if you want, but it is
not required by code. If plumbing is installed to code, there is
little worry about a lawsuit. Kinda hard to sue when the plumber is in
compliance with prevailing codes.
And NO, you do not put the water closet as close to the vent as
possible. Again, code requires that you do not tie into the base of
that stack within 10 pipe diameters. Which means if you are running 3"
pipe for the WC, you must not tie anything in within 30" because of
the hydrostatic current.
The code is NOT a re-invention of the wheel. The prevailing code is
the culmination of THOUSANDS of years of trial and error. There is
little in the codes that I find to disagree with. And frankly, even if
you do disagree, you are still required to install that system to
code, not to the specs of the national bureau of standards.
The code book I use is different from the code book others are using
because most states have their own interpretation of the code. In my
area, frost is not a real problem. We can bury water lines 12" below
the surface. Try to buy your water lines at 12" in New Jersey and
you'll be digging those lines up and replacing them.
Don't argue with the code. It is the way it is for a reason. Don't
deviate from the code. Your local inspector will FAIL YOUR INSPECTION.
And your local inspector does not care to hear a single word about the
National Bureau of Standards. He's simply going to mark your card
FAILED and walk away. That code book is our bible. If it isn't in the
code book, I can't enforce it.
The only thing I would change in the code book is that yes, I would
personally like to see a return to at least one full-size vent. If for
no other reason, it makes access to the system possible through a roof
vent. I would also change the code regarding your washer box. I would
write the code to require a 3" drain pipe vented with a 2" vent on the
washer box (ie, 2" trap dumping into a 3x2x2 tee).
DON'T FUCK WITH THE CODE.