I think it would be morally wrong of you to accept the financial support of your parents in order to be able to save for a secret new life you know they will be upset by. If you want to be free to pursue the life you want, good for you, but do it on your own nickel.
I think you are currently too young and immature to get married to anyone.
I think the rush to marry primarily because it's what your your partner wants is evidence of your immaturity.
I think the fixity of your thinking about most of the detail of this plan is further evidence of your immaturity, i.e you won't move out, you won't rent, you have an advance plan in place in the event of marital breakdown without any apparent understanding that that is not how such things are decided.
I think it's ironic that your thinking is so fixed when your key problem with your parents is your belief that their thinking about you and your sexual orientation is fixed.
As a parent of adult children, I can tell you that we can handle just about any unexpected and even unwanted revelations, but what is harder to row back from is secrets, lies and deliberate divisiveness.
Tell them or don't tell them, but don't use them. And don't get married.