Explain how cobra works for current kidney stones

My husband left his job, yesterday was his last day. His new job waits 30 days until insurance starts. I am currently being treated for kidney stones over the last 5 weeks. I have a kidney stint in. I plan on getting on cobra as I have already met my out of pocket max. Questions:

1)what happens if I have to go to the ER for the stones?

2) Dr is ready to remove the stent however is concerned if I have to go to the hospital after for a stuck stone, that I won’t have insurance coverage.

3) I am going to need a through the back surgery to remove these stones since nothing else is working. How can I schedule this if I haven’t been able to sign up for cobra yet? Do I have to wait until we get the paper work to actually do any procedures? Is cobra just good for emergency use until you get signed up?

4) Do the (3rd party management)companies for cobra health insurance usually send the forms via mail or email?

5) can I pay out of pocket until my Cobra kicks in and then gets reimbursed?

6)can someone explain the retroactive to date of last day employed and how that works if in the middle of treatment. I see a lot of people saying they just wait and see if they use the insurance before doing cobra, however I need a procedure and surgery done that can not wait. I need that cobra asap.

7)I feel like I’m covered if I go to the ER but not covered now if I need my stint out or to go to my Dr or specialist that isn’t an emergency. Also my assumption is I would not be able to get anything pre-approved since I wouldn’t show up as insured?

8) if my husband puts me on his new insurance in 30 days, which becomes the secondary insurance? Since I’ve met my oopm I don’t want the new insurance billed and have to pay that oopm as well.

Thanks so much.