Yup, I have to agree with the rest. If you've been to vegas 50x and gamble what you say you gamble I'm sure that you are on someone's radar already. You should check with your "home" casino in vegas, I'm sure you would get some of what you ask for if you do gamble that amount. On the other hand, if you are just saying that you would gamble that amount but don't really gamble that much on your other 50x trips then you shouldn't count on getting anything upfront. $50k upfront money means squat to them, it does put you on their radar but they will look at your gambling history to see what you've done on previous trips.
Best to contact a host to see what they will give you but again the host will check your playing history to determine comps. If little to no history the host will tell you to pay for your own room and everything else and charge them to your room, then at the end of your stay go see them and the host will determine if you deserve to get any charges taken off your bill. Get and pay for your own limo going to the hotel, unless you have a history of play at CP or their sister properties which warrants the limo they ain't going to send the limo for you. Same thing with the spa, VIP entrance and cabanas, charge them to your room and at the end they will determine if your play warrants removal of charges.
Vegas knows better than to give carte blanche to people who "say" they will put in play but don't have any history of gambling so don't expect to get anything if you don't have a history at that casino, even if you flash them upfront money.
I agree with others, if you are going with your GF I don't think she will enjoy watching you play on the tables for hours every day to get the comps (you will probably have to put in at least 3 - 6 hours a day to rate those comps at CP) and you will probably be spending more time showing your GF a good time in vegas. It would probably be best if you use some of that $50k to give her a good time instead of worrying about playing for comps.