So sorry to hear about your situation, Katarina.
BUT, I'm super proud of you for finding a dentist and having the courage to start having your teeth taken care of again. As a phobic, it's pretty certain that you'll never be completely "ready" for a dental appointment, but you should be sure to talk to your dentist a lot about what to expect and how you'll feel, etc. Lots of people have multiple teeth extracted in a single visit and have found it pretty easy. So, there's probably no physical reason to not get it all done at once. I'll assume your husband's objection is just that it will be too emotionally draining for you. Just remember, if your dentist gets started and you're having trouble handling it, you can ALWAYS tell your dentist to stop. So, if you're ready to get started, I'd recommend just proceeding, and ask your dentist to check with you as she goes along.
Laughing gas is pretty mellow. You'll have a little tube in your nose that will blow what feels like cool air, and it just helps to calm you down. You probably won't really notice anything-- it doesn't knock you out or make you feel "high" (usually)... just focus on breathing deep, and let it do its thing. Your dentist will still give you local anesthetic (i.e. "novocaine" although actually it's a newer -caine cousin) to numb your nerves so you don't feel any pain during the procedure.
Most people are surprised at how easy extractions are. It's nothing like the image you have of someone tugging and pulling. Actually, the dentist will push on the tooth to rock it slightly from side to side. This causes the ligaments to release their hold on the tooth, and usually, it almost falls right out on its own, without any pulling. The sensation is a pretty strong push that you almost have to lean into a little, but there's no pain involved. Many people like to bring some headphones to play music to distract them a little-- that and focusing on your breathing will get you through. It only takes a couple of minutes to extract a tooth.
I was terrified when I had a molar extracted last year, but actually, after they got me good and numb, my dentist pushed five or six times, and then said, "And that's it!" I didn't feel any pain, not even a tiny bit, and I didn't have any sensation of anything coming out. When they sat me up and told me to go home I thought something had gone wrong! But my dentist said, "That's it, you're done!" It all took maybe 10 minutes.
You'll want to plan on soft foods only (applesauce, yogurt, pudding) for the first 48 hours or so, and no smoking or using a straw. You'll also want to rinse very gently with warm salt water a few times a day to speed healing. And take some ibuprofen as soon as you get home, before the anesthetic wears off.
Good luck and hopefully you get some more good extraction stories from others on here who've had multiples. You'll certainly be tired from all the stress and anxiety leading up to it, but I think you'll be surprised at how easy and painless it is. Good luck!