I'd say "una casa NELLE Marche" (withouth "che sia": it is not wrong but it is unusual in this context), while it is ok to use the subjunctive after "è importante che".
Tip: we usually say "Cercasi" (the impersonal form) AND I would add "cercasi villino o appartamento", if you want to specify the type of dwelling, because what you call "house" is "villino unifamiliare" while "casa" is more generical and indicates all kinds of dwelling, including houses, flats, terraced houses, etc.)
Last but not least: "BisognA usare" (impersonal form, "Is it necessary to use...?") or "Devo usare" (="Do I need to use...?")