DIYbanter - Island sink vent loop questions

Hello,

I'm planning the DWV plumbing for a kitchen island sink and have a few
questions about the requisite vent loop. We're on the 2006 UPC here
and air admittance valves are not allowed. I'm using the following
image as a reference:
http://www.rd.com/images/tfhimport/2003/20031001_Ask_Handyman_page001img001_size2.jpg

(1) The drain line will be 2". Is it necessary or useful to enlarge
the vent from the usual 1.5" to 2"?

(2) I assume that there is no horizontal separation requirement for
the two vertical legs of the loop. So from the fixture san-T I can
come up to a street 45, a 90, and then a street 45. Is that correct?
Also, is that a vent 90 or a long-turn 90?

(3) Is it important that the vent leg of the loop connect to the drain
downstream of the drainage leg of the loop, rather than upstream?

(4) To get both the horizontal vent and the horizontal drain to fit in
the joist cavity, I'd like to minimize the height difference between
them. In usual pattern, the vertical vent leg comes down into a san-T
for the horizontal vent take-off followed by a combo to tie into the
horizontal drain. I'd like to roll this san-T/combo over to 45
degrees from the vertical, by inserting a 45 elbow before the san-T.
Is there any problem with this? I assume that the prohibition on
"flat venting" would prohibit me from rolling this over any further.

FWIW, there will be a regularly vented sink upstream of the island
sink, and I plan to run the island vent over to the this area to
connect with the regular sink vent. Thanks in advance.

Cheers, Wayne