Within 24 "
Yes if the vent pipe is 4" and vertical by code and there is nothing connected between your toilet tee and where you would connect your new toilet tee. If not worried about codes then yes you can connect to a 3" vent line if no other vent lines are connected down stream. If you have a vent pipe that is less then 3" and or you have other vents connected between your old toilet tee and your new toilet tee then NO you can not connect a new tee for your toilet.
Yes.
partially clogged drain or vent, improperly installed vent or drain
gas gets trapped in the drainage system if you don't vent it (and you don't want that gas coming back into the bathroom)
No, that is why it is called a vent pipe not a soil line
Within 24 "
Yes if the vent pipe is 4" and vertical by code and there is nothing connected between your toilet tee and where you would connect your new toilet tee. If not worried about codes then yes you can connect to a 3" vent line if no other vent lines are connected down stream. If you have a vent pipe that is less then 3" and or you have other vents connected between your old toilet tee and your new toilet tee then NO you can not connect a new tee for your toilet.
Yes as ALL fixtures need to have the vent placed above the FLOOD LEVEL RIM
No
Who needs a toilet
Yes.
partially clogged drain or vent, improperly installed vent or drain
Any vent is usually the size of the drain or waste pipe it is connected to. 3 or 4 inch on a toilet.
Should be individually vented
As close as possible is best, but there just has to be a vent so that the air that is in the line has somewhere to go so that the liquid isn't trying to compress it. The closer the vent is to the toilet, the better it will flush.
Yes. You need to open the plumb, & you have an air vent there.
Every toilet should be wet vented with the sink in the bathroom.