My first piece of advice is to take a deep breath.
My second is to really consider what you WOULD be willing/interested/able to do/be in life. Not what you think you can't handle.
I say this because when we focus on the negative-we create more negativity. When we focus on the positive, we create more positivity. There are other threads on this so I won't elaborate here.
My third is go pick up Opening Up. It's not a GREAT book in my opinion. But it has one feature-if you read nothing else-that IS GREAT for where you are right now.
That is-it lists TONS of different details that should be considered before opening up your marriage in any manner. It goes over all sorts of details you might not think of and very thoroughly.
THAT is very helpful for my next piece of advice.
My fourth piece of advice is to start working on a boundary agreement. That is-a RIGHT NOW we agree to these limits/privileges, ending with "and we agree to re-address these for possible changes/updates monthly for the next year.
Please feel free to ask more detailed/specific questions.