Sending an email with the information from a process start form

I feel like there is some detail missing here.  The generic answer is fairly straightforward though: your Process Start Form would pass pertinent data into the Process Instance via PV parameters (the normal purpose of even having a start form).  Then in your process, either immediately or later-on, you would have a Send Email smart service node, and you would reference the data originally passed in as PVs to construct the wording included in that email.  There are myriad different ways to do this depending on the specific requirements, though.