I would use this method instead: How to Use Marketo Forms to Register Multiple Event Attendees The server-side form post method isn't supported and is extremely error-prone.
Our blog has a lot of examples: http://developers.marketo.com/blog/ One specific one would be sending operational email: http://developers.marketo.com/blog/sending-transactional-...
You can pull info from the opportunity via scripting tokens. In this case you'd probably want to pul the name, and any other info, from the $TriggerObject. You can read more here a...
I'm sure this would be quite interesting. I imagine that we have integration partners capable of integrating both platforms. I would check Bedrock Data, Talend, Tibco, and Mulesoft...
I can't see anything wrong with the request itself. If you try to get the lead by ID before or after trying to make the campaign request are you getting a response for that lead?