Hi @deedeedee - try not to overthink it - it is usually minimally invasive ....
I had a lumpectomy 2 years ago (close to my nipple) and had no real 'worries' - and my scar healed really well, with not much scarring. I was glad I had a small oblong cushion with me tho - to support my arm after surgery (in the hospital) and for the drive home (supporting bumps on the road & driveways on the way home. Make sure you are hugging it for the whole drive home.)
If you are staying in over night - I'd recommend ear plugs and eye masks (like you get on long haul planes.) Hospitals are noisy, brightly lit places!
Make sure you take any medications you may already be on - you will need to give them to the nurses to administer to you, so it doesn't affect anything they may be giving you for pain, etc.
Do you live in a bigger city or are you rural? If rural, you can claim back for the cost of fuel etc to get to your appointments.
take care & all the best for tomorrow xxxx