Look, RIFTS is huge. Rifts Earth alone has, what, a dozen sub-settings spread throughout the post-apocalyptic globe? The Lunar Sphere (i.e. Orbit) and the Solar System add a few more, then there's the other dimensions and the cosmic sub-settings. Of all Palladium's games, this one truly is a kitchen-sink play-anything product line. That's a lot of stuff, and without care taken you can end up with an undesireable mess that's no fun.
You need to curate. That means sorting through the stuff and choosing what to allow and what to cut out, with the result of forming a collection of stuff that adheres to a theme or motif which binds the collection together into a greater whole.
In terms of house rules, it's this simple: "Players may not access any content that the Game Master does not own."
No races, no Occupations, no gear, no locations, no powers- not one damned thing can be had unless the Game Master owns the stuff that such a thing comes from. Loaned books and free PDFs do not count; only physical copies count. This makes the curation process easier; the GM only has to work with what he actually has on-hand, and not deal with requests from players to be whatever.