hi, i just came back from the vet and she said that it's not a prolapse... it's a tumor

the lump actually not coming out from inside, it's above the vagina.. and then she told me about the surgery and costs which will be cost more less $250! (incl. spay)
now i haven't decide yet, but i'll share what the vet did mentioned about the surgery:
#1 She prefer to get Jojo's blood tested in lab
#2 The surgery to cut the tumor
#3 The thread cost to stitch (tumor and spay)
#4 The drug while surgery
#5 The spay surgery
#6 The antibiotics
and those has not finish yet, if Jojo is weak after the surgery, then she must stay at the vet which will add the bills.
So before i decide any decisions, I have a few questions:
1) As you know, once your pet has a tumor, even it has taken away, there are chances for Jojo to has another tumor. How big the chances is depends on how bad the tumor is now and the vet has no idea about it until she had a surgery. My question is, is it possible to know how bad the tumor before the surgery?
2) Are the vet's actions which I mentioned above are proper? I mean, is there any other way to cure Jojo?
3) Are there anything I should do to prevent the disease spread to anyone or other pets? The vet suggest me to wash hands after touching Jojo and get her the diapers
Thanks for the infos and advices guys, appreciate it a lot
SW