You say "if my B30 comes" so that means you don't have one offered yet. You also said you wanted to keep the classic flap because it's a classic. If you sell your classic flap to an consignment store, most stores will take a 30 - 50% consignment fee. If the birkin is offered, can you still close that gap? If you regret selling the flap, it will cost you more to buy it again.
The classic flap is not quite roomy, birkin 30 is. Do you have experience with a leather tote? They can get heavy. Does that match your lifestyle? Did you ever tried out a bag of the same size and weight? Tried out as in actually used it for at least a month or so. A bag can feel very different if you are trying it in a store or actually fill it with your stuff and use it.
These bags are so different and to me it's not quite clear why you want this. It looks like you want to get rid of one to fund for another, and that is okay, but why do you want a birkin? Why do you want a handheld tote? Why do you want a 30? These bags are so different that I would say keep the flap and get the birkin money elsewhere. Also because it feels like you want to sell the flap for funds, not because you are done with the bag in general.