I can only tell you that the Elgato Camlink is only compatible with quad core systems and up. I believe a 2009 macbook or imac for that matter is only dual core. So the camlink will not work on that system. However you might want to look at the cheap china capture cards. They often use USB2.0 which might work on your 2009 macbook. But do your homework before you buy. I don't guarantee it will work.
As for a camera, you need a camera that had "clean" HDMI output (this means there is no text overlay or focus information/squares in the image when you view the HDMI signal) and it needs to be able to stay ON for an unlimited time (much camera's turn of automatically after a certain time, which in some cases you can turn off).
It's also worth it to see if autofocus works while in "clean HDMI' mode. In my case, i can only get clean HDMI when i turn autofocus OFF (Canon EOS D800/T7i)
You might want to have a loog at the elgato camlink compatibility list to see which camera's have clean HDMI etc. Most camera's that are suitable are on their with additional helpfull info. Just google for "camlink compatbility list"