Can you tell me more about file uploads?

Hi, we want to create a new form primarily for clients to send us files.  I noticed when I add an upload filed, it only allows 1 file to be added. If I add another, it replaces the first. Thus, my questions regarding file uploads. 

1) Can i put multiple file upload fields on one form so a client may attach several files at once?  

2) is there a limit to the file size per file they attach? 50 MB, 100 MB, etc?

3) How about a file upload maximum per form submission?  How about per month?

4) How long do files stay on your server until they are dropped off?  Once we download the file, we no longer need it but I wasn't sure of the time length you keep it. 

We may also use the drop box option so your file size issue may not apply, although i would still want to know about question 1. Thanks!

David Midler