1) Does the sponsor only have to get his info page of his passport notarized, and this has to be done by a UK notary?
Yes, only his info page with the photo on it, but, no I believe it can be done by a US or a UK notary (it's cheaper in the US).
2) And send in his original long form birth certificate? Or can that be copied and notarized too?
No, the long form birth certificate is not needed at all if you are sending a notarised copy of the passport page. It is only needed if you don't get the copy notarised and just send it as a regular photocopy.
There are 3 options for sending the sponsor's passport:
1) Send the actual passport (not recommended if he will need it to travel though)
2) Send a notarised copy of the photo page (can be notarised in UK or US)
3) Send a regular photocopy of the photo page, but you will also need to send his original long-form (A4 size) birth certificate to prove that the information on the photocopy is correct and true.
If you do options 1 or 2, then you do not need to send his birth certificate at all, in any capacity. If you do option 3, then the birth certificate must be the actual, original one because it is being used to prove that the passport photocopy is real and not faked.