Adsense & Multiple Blogs - How to Properly Configure?

Hello all. I've had about 100 domains dormant for a while. My VA is putting up basic content sites for me and I'm adding Adsense to them.

I've gone in and created 100 Content Channels based on the domain name

I've gone in and created 100 Search Channels, also based on domain name

I've done this so I can track which domains are producing $ and which I should possibly let go when the renewals come up.

My question is this....

If I create 4 different sized ad units, can I use those 4 ad units (and the corresponding Javascript) on every site, or do I need to create 4 ad units PER CHANNEL (i.e., 4 x 100 = 400 ad units)?

I do not particularly want to create that many ad units. I just want to know if I have to (or if I "should", then why "should" I ?)

Or will having 4 ad units and using that same code on all 100 sites be fine, and what I did setting up 100 channels by the base domain, ie.: example.com -- will that be enough to (1) serve ads and (2) track by domain.

I'm thinking:

- By creating 100 channels and using 4 ad units, I can track how each site does, and separately how the 4 ad units do, but I won't be able to narrow down to how much each ad unit made for each website.

- By creating 100 channels and using 400 ad units, I can track how each site does, and separately how each ad unit did on the site.

Is this correct?

Thanks!