Ranking With Multiple Keywords

Hi

I have done pretty well so far getting high amounts of traffic and decent rankings for wordpress websites built around a single keyword with an absolute match domain name. I am starting to build a few review sites that target a range of products meaning I'm going to have to try and rank for several keywords rather than just one.

Is there any implications of doing this with wordpress? I assume the best way is to register a domain name with the root keyword and then write posts for each other keyword with a mixture of supporting keywords and sprinkle the root keyword a few times in each post too?

Once I have a few posts is it best to organise these using category menus, tag menus or page menus or does it not make much difference?

Do you find it more difficult to rank in a high position for each keyword when the post is essentially a separate page on a domain with the root keyword?

Obviously it depends on competition too, but in general would this structure and strategy have any major implications?

Any advice or help appreciated!

Thanks
Tim