Research Tasks List
Catch 3 Pidgey or Murkrow.: 5 pokeballs
Catch 3 Swablu: 1 Pinap Berries
Catch 20 pokemon with weather boost: Ninetales
Answers
Agree, unless the reward is good, or it's something I'm literally about to do (like win a raid as I'm getting ready for a raid), I pitch'em and look for good ones. Pinaps and razzies are useless, 5 regular balls is weak, sometimes I'll do 5 great balls. Knowing which encounters are good is key - I did catch 10 Pokemon for an encounter, and got Magikarp, which is great since I need candy for the Mew quest. Knowledge is power, after all.
Depends on the current spawns around you, with lots of pidgeys and swablus, that is just a few minutes, and balls and berries you consume at a high rate so they are always handy.
As for the last one it is also done very quick and see Ninetails as a stardust bonus (I expect it gives stardust when caught, doesnt it?).
I prefer to do quick and non-optimal tasks, and get done with them, instead of getting it every time I later spin that stop.