Hi,
first, it would be most helpful if you sent your question to sales@avast.com (or any other contact emails you have) in the first place. We have staff that is trained in this, and will easily help you.
Anyway, I think I can help you too...
1. ADNM pricing:
http://www.avast.com/eng/adnm_pricing.html2. What to download: if you want to use ADNM and the managed clients, you only need to download the ADNM package. During installation, the avast management server will create a repository of all managed products, and will you install the agents directly from the repository.
3. About SBS. I suppose that by "Pro" you mean "Premium"..? There's just two types of MS SBS - Standard and Premium.
SBS has special licensing to lower the costs in small network situations (it's sort of a bundle for good price). However, in your scenario, I don't think it would be wise to bother with the SBS license. Use regular Server Edition instead.
I guess your best bet is to go with the avast Standard Suite (170 lic), OR, if mail server scanning is also required, the avast! Advanced Suite (also 170 lic).
This will cover all your machines (and up to 18 servers).
Thanks
Vlk