Yes, drop-down selects are no problem. Just put something like this in the &recipientArray property:
The readme.txt file in core/components/spform/docs/ has fairly complete explanations. You can also look at the property descriptions on the Properties tab of the snippet by clicking on the little plus sign next to them.
There’s a tutorial at the site in my sig., but it was written for the Evolution version and would probably do you more harm than good. I’ve been meaning to do a Revo tutorial, but haven’t found the time.
One caveat: The install needs to be updated for the current version of MODx. I think everything critical is installed, so you should be OK. It should create a contact page and a "Thank You" page for you, but it might not. It should work out-of-the-box once you set the &recipientArray. Let me know here if you run into any trouble.
You can put your own text on the page above the form, but don’t even think about customizing the form (except with CSS). It’s not really designed for that.
If you need SMTP, I’d advise using the MODx system settings rather than the SPForm SMTP properties.
Let me know if you run into any trouble.