I would go for 3-1-3-2-3. After lvl 5 its a matter of taste and situation. If you want to gang a lot you should max. out 1 and eventually get your ult. If you want to farm instead go for 2 + 3 and skip lvling ult. I always prefer ganging potential over farming.
The move shown in the vid is no longer possible. You can now earliest pull at 53 seconds without risking the pull to fail. Never the less you can still pull 2 camps.