@rafcer I've had an ostomy since 2002, its an ileostomy, but I had many of the same questions you have.

I wear normal underwear, but high waisted ones. This supports the weight of the ostomy pouch for me. What works for you will depend on what kind of underwear you like and where the stoma is situated. For most women the stoma is below the waist, and slightly below and to one side of the navel.

These are great questions for the Ostomy group, where this discussion has been crossposted
https://connect.mayoclinic.org/group/ostomy/

@rafcer My stoma is about 2 inches below and to the right of my belly button. I wear high wasted panties and a belt that attaches to the pouch for extra support. My clothing is pretty normal size but not tight and the device does not show. No incontinence but I did have post surgery fluid draining from my vagina for several months and needed to wear a pad. The amount of fluid decreased over time. I had robotic surgery , not open surgery so everything was done with six small incisions and removed through the vagina. Initially used a wound care pouch that can be open and closed and then graduated about 2 weeks after the stents came out to a normal pouching system . I don’t wear anything else to protect the stoma. Im guessing you will see an ostomy nurse as part of your surgery prep. They will assess and mark where to place the stoma and will help you with questions too. Also had visiting wound care nurses for about 1 month after I went home to assist with pouch changes until I got the hang of it. The hospital ostomyb nurses also gave me an initial set of supplies to go home with and made recommendations on what to use and taught me how to care for the stoma before I was discharged . Best wishes and hope you have an easy recovery!