I am a Canadian Immigration Consultant, and cannot advise you on USA Immigration matters. However, in terms of ethics, your path to legitimate immigration is not via a marriage of convenience. If you have the chops to make a start up work, that is legitimate. If you have a job offer and can proceed via the L1 visa, then this is likely your least complicated route. "Ethical" immigration is universal, and so I my answer is given to you in this vain. Marry for love, not a visa!