I don't think the OP is copying, they make that clear - unless person in big space-suit with big gun is copying, but on that level, *all* games have to build upon existing ideas - few games out there are 100% totally original ideas, because that's pretty much impossible. To those people who say they prefer original games, what games are you playing that are totally original?
Not to mention that Games Workshop took loads of their ideas from things like Lord of the Rings (e.g., Eldar based on elves, not to mention all their more traditional fantasy settings). Space marines are also a copied idea and name. Not that there's anything wrong with that - it's good to build on existing ideas. But I disagree with the idea that Warhammer is somehow original, yet anyone else is just copying from Warhammer.
Ideas aren't covered by copyright - but you do have to worry about things that are covered by copyright, as well as trademarks.
As for what to do here, it seems an obvious thing would be to avoid "40,000" as it just creates an obvious target for yourself.
No one can really answer whether you'll be sued - you can be sued by anyone, even if their claim is dubious. It's about minimising the risk to your project.
the fact that you're using names for units that are like those found in WH40K
The OP says "we will NOT COPY the Units/Names of the Warhammer/Starcraft/Startroopers Universum". Certainly yes, using the names such as Eldar would be a bad idea.