Hi Jacqui,
Unfortunately, you've been tasked with a difficult task. Writing your own web service, deploying it, maintaining it, is no easy task for an InfoPath/SharePoint beginner. The topic has been discussed before in threads this like one. In addition, to upload a document (I assume into a separate document library) requires custom code.
Where to start? You could probably design a blank, new form, add your nodes, design the canvas (view), publish to the browser and add a submit data connection to the form library. That's the easy part and will get you some understanding of InfoPath design and SharePoint deployment. Once you've got that working, you can move on to the hard stuff: writing the code to upload the attachment and writing the web service to submit to SQL. We have a sequence of 4 training labs, available here, for those new to InfoPath.
Come back as you progress and ask questions. Good luck!