a) Yes. We are using CR (earlier version) to report against Domino data via a browser.
b) One method: Put all desired types on the report, in different sections. Have user select in the report options from a list, and suppress the other graph sections based on that selection. Not very efficient, as CR will build the graphs anyway, but it will work.
c) From the CR viewer you can export to a number of formats. In the version we’re running, PDF, Excel, Word, Crystal, Txt.
Before you lock in on CR, unless you have already spent the money, look at what MS Reporting Services and Proposion’s Report Adapter for MS Reporting Services can do. It may get you where you want to be for less money and pain. There are other reporting tools out there as well that may work for you.