Some questions about veno...

I used to play carry heroes because everybody loves the big numbers and the big kills but recently I've decided to broaden my horizon from just carry and tank to pushing and support.

I randomed veno a few days ago and was pretty good at just pushing 'the other lane', the one not occupied by any heroes at the time but I have a couple of questions that I think will just make my veno pushing better:

-Where exactly is a good plague ward placement if the creep wave is fighting in the middle of the lane?

-Early game how can I aggressively push the enemy heroes back without dying/feeding them plague ward gold and xp?

-And lastly, at towers, what is a good plague ward placement? (both offensively and defensively)

Any answer is appreciated as well as pointers to good games that showcase what you are explaining:)