No need, just use the master configuration. The PIX will throw away the comments as it reads them.
Yes; see my other reply in this thread about how to do this nicely.
Unreliable. The PIX does not have a big telnet buffer; you would have to do small sections at a time.
Also, in the other posting I said that tftp files are read as if they were in "config terminal". That is not completely accurate. For example, if you had a comment that included a ? (question mark) and were to copy/paste that into a telnet session, the ? would trigger the PIX help system; when you tftp, that does not happen. And most commands in the tftp'd file have to be full commands, as it will not do command completion the way a telnet session would.