言うだけでもなんなんで。
よくわからんがバージョン依存あるかも。
あー、書いてたらアイスとけたよ

tell application "Finder"
set theFileList to selection as alias list
repeat with i in theFileList
set i to i as alias
set i_Extension to name extension of i
set AnswerFileName to my getExif_(i) & i_Extension
set NUM to 1
repeat while (exists (file AnswerFileName of parent of i))
set AnswerFileName to my getExif_(i) & "_" & NUM & i_Extension
set NUM to NUM + 1
end repeat
set name of i to AnswerFileName
end repeat
end tell

on getExif_(theFile)
set theName_of_Camera to do shell script "exiftool -model " & quoted form of POSIX path of theFile

set theDate to do shell script "exiftool -DateTimeOriginal " & quoted form of POSIX path of theFile

set OriginalDeliniter to AppleScript's text item delimiters
set AppleScript's text item delimiters to ":"
set theName_of_Camera to item 2 of text items of theName_of_Camera
set theDate to items 2 thru end of text items of theDate
set AppleScript's text item delimiters to OriginalDeliniter
return text 2 thru end of theName_of_Camera & (theDate as string)
end getExif_