Hey Sandra, 

1).  It depends on the FYI statement.  If it is to
help you with something (ie "FYI - This cel is
from episode 48 scene ----.), then I would tell
them tahnks.  If the FYI is nothing more than a
RUDE degrading e-mail (well, you can imagine what
one may be like!), then I would not respond to
them and forward the e-mail to Ebay for harassment
and obsene language (they have a policy against
using the question form to curse someone out).
2).  Most people who buy an expensive cel would
want to see a large scan of it, BUT, most people
do not have DSL and it would take 20 minutes to
load in your auciton and they will lose interest
in it.  So, just leave the option open if they
want to see a larger scan, but don't use too large
images for your auciotn.

Hope this helps.

J-Decker