few questions about vent:

1. vent will go up but can i start up but immediately go horizontal few inches and then go up?

2. can I horizontally U turn (the bottom of the U is more than 1 foot) the vent and then go up?

3. Is there any limitation on horizontal length of a vent? can run a vent 20 feet horizontally and then go up again?

4. what's the vent pipe size requirment? 1.5" for bath (what I have now)? 2" for others, 3" or 4" for main stack and entire house?

5. one 2" vent can serve how many fixtures?

6. when add a vent to my 7 feet long counter sink drain, can I add it anywhere less than 5 feet from the sink side or I have to add it immediately after the p-trap?

thanks,