I doubt if the majority of alien life will be drastically different from life on earth. If you study evolution you'll find that there tend to be evolutionary trends in a given environment. For example, there are species in the Antarctica that are like those found in the Arctic, separated by a warm water barrier. Either they found some way to cross the barrier or they both evolved separately then became like each other because of their environment.I can't say much on the food issue, I'd hope any aliens that lived in space would have some self-renewing form of sustenance rather than feeding on whatever they find while they're out there (because there usually ain't much out there). If they were attracted to earth because earth happened to have something that they needed that other planets didn't, well, mankind is doomed.
Also, as for the scenario of two races fighting over the MOO2 equivalent of a "huge UR Gaia world", two species from entirely different planets are unlikely to have the same ideas of what an "ideal planet" would be. One race might be happy in -200 C while the other is happy in 2000 C. One likes to eat fish and the other likes to eat rocks. One lives on land and breathes air, the other lives underground like worms and enjoys toxic gas. Chances are slim there'd be mutual appeal.
The only thing they might have in common is a desire for building materials, but in space, they'd be all over. Unless the aliens have a particular need for wood.
When it comes to intelligent life, if their home world is anything like ours, there's no reason they couldn't have similar needs as we do or even look like us. I have read accounts of people claiming to have encountered human looking aliens.