Sofia... if this is an offer you are personally considering ...
1. Make sure you know how much money this old guy really has ... available, not tied up in a trust to some grandkid. Running out of money afterwards is not fun. Demand an outside auditor to prepare a new set of financials on your new fiancee. Remember, No romance without finance!
2. Resolve all legal concerns: does he have grown children who can contest the will, have the will changed to include you BEFORE the Wedding, if he wants a prenup... have your lawyer write it.. just to ensure it is equitable.
3. Reach an agreement before the wedding on what your responsibilities will be (how often do you have to do this old guy and exactly what you have to do). In return have him set aside a suitable amount of money in an escrow account, in case him or one of his pissed off adult children decide to deny you your just rewards for your sacrifices with a prolonged court battle.
4. You will need a written Maintenance Agreement; this should include your monthly Clothing Allowance, monthly Jewelry Allowance , Personal Needs Allowance, and monthly Car Allowance. These should all be set at a percentage of his net worth.
5. Insist on documentation of your right to handle all hiring and firing of home, personal, business and office staff ,including but not limited to the "Pool Boy".
I'm not an attorney like Civil Barrister or anything... This is just the stuff I remember so well from last time.... I still kinda miss her though...