CTH, PTH, ToA and NW ELB strategy question (in General)

I'm still thinking about all that Archery-Stuff, but i'm unsure in how much it actually gives me.

I also don't really understand in which order all the modifiers are put.

So here some thoughts, pretent my ELB has +100 (e.g. +30 and +70 from the ToA):

CTH with Archery would be:
+100 + 100BTH = 200%

CTH without Archery would be:
+100 + 20BTH = 120%

right?

Where would the ToA bonus be added to? Does it make any difference at higher levels PTH? Or is it right that the ToA bonus at higher levels becomes less important as single + costs more?

No archery penalty also applies to PTH.

oh wow, ok

.. well, than there is really no choice ..

Yes

Using a bow without archery is wasting a minion and the nw on it.