1) no, they count as turrets and as such need an active lock.
2) not 100% sure but tractors come in small and capitol flavours so id imagine smalls have a limit as to what they can pull.
3)again NO they are for pulling wrecks/cans, not for interdiction purposes
thats the job of Webifiers/ Warp Disruptors etc.
4a)yes ,tractors pull at 500m/sec so as long as your not speeding away from wreck faster than this it will get to you (or allow you to position where you want).
4b)no, weapon locks are lost when you enter warp and as such tractors have nothing to pull without the active lock so are turned off.
dont you hate when someone else posts during you typing a reply