If you pull all the data from each SFDC object individually (leads, campaigns, opportunities) and then link them normally in the QlikView data model, you should be able to see everything. The order of which you load the tables doesn't matter.
Unsure what you mean by "how the end user inputs data into SFDC".
Can you provide some more detail?
- Are you using the QlikView SFDC connector or a third party connector?
- What of SFDC org are you using? (enterprise, professional, etc)
- Do you have sysadmin level API access, or is your login filtered by the SFDC security model?