If I settle down and build a beach house at the edge of Mare Imbrium, does it need to be up to code quake-wise,
Your bigger problem would be finding a beach. 
Beaches aplenty. Water at them? Priceless. 
I guess my first question is which building code are you using … which immediately brings us to the jurisdictional issues … launching from California gives you the advantage of having access to more modern technologies, but then you’ll need to comply with their more stringent earthquake mitigation requirements … whereas launching from Povertonia allows far more lenient code compliance but you’d kinda be stuck using adobe bricks for construction …
I think you’ll find getting homeowner’s insurance the biggest obstacle … things like your new home being air tight isn’t normally covered in building code but I’m sure your insurance carrier will require it … clear-cutting the jungle back 100 feet for a “defensible” space in case of forest fires … a sea wall to combat rising sea levels if you decide to carry flood protection … the list goes on …
Alternately you can bring some guns along and hold a Sovereign Citizen position … I’m not a lawyer but I think that might actually work in a court of law … if I understand the international treaties you’ll only need to be conducting some bona-fide scientific research there … I’m absolutely sure I’m not the only one who thinks it’s of critical importance to know if cats spray as much in the low-G environment …
Let me know if you plan on renting out the spare bedroom … I’m interested …