OK, first off, any question you don't know the answer to ISN'T a dumb question.......
Unless you don't ask it!!!!
The fuel is drawn into the carbs by way of vacuum, only when the bike is running.
There is no need to turn the petcock off.
Most here use Seafoam as a fuel stabilizer, fuel system cleaner. It's often suggested to run it every 3 or so tankfuls at about 3 oz per tank.
Exact measurements aren't necessary. Just guesstimate. Too much wont hurt anything.
Most here also recommend NOT
I'd say if you bike is going to sit for more than a month, add atleast 3 oz of Seafoam, take the bike for a ride to get the Seafoam through the system, then park it.
Any other question, just ask.
Most answers can be found using the search function
, but that can lead you to so many results that it's sometimes hard to find the answer you're looking for.