IMO
140 max for thumbs - K size is not so imp.(but you cant have 400K thumbs
yes I have seen this) good thumbs will save you bandwidth
Up to 800 for pics - as long as K size is reasonsable
Anything greater than 800 pixels long side or greater than 80 K would usually get rejected
Anything greater than 1000 pixels long side or greater than 100 K would definitely get rejected
DD