I'm a tandem nurser and have been for 2 years now. I'm nursing a 4 yo and a 2 yo. When my second son was born I was so thankful for nursing. It really helped my then 2 year old to cope with his new baby brother. We'd just snuggle up on the couch and I'd nurse both at the same time or nurse the baby first. At times there was a lot of whining, "I want Mama's milk!!!" or he'd jump up and down on the couch begging for it. But if I hadn't nursed my toddler at the time I think I would have resorted to giving him unhealthy foods or candy to keep him calm. All he really wanted was Mom's affection and attention. I didn't have a lot of outside help, so I just pulled him nearer to me (instead of doing timeouts for bad behavior or yelling at him). So he nursed lots and got all the extra nutrition and tons of comfort and cuddling. Tandem nursing just made parenting easier for me.
This isn't to say it was super easy all the time. There were lots of times I felt overwhelmed, but I realized it was temporary and just took things day by day. By the time the baby arrived I had night-weaned my first son. He then slept with Dad in one bed and the baby and I slept in another bedroom. We tried to make it work in the same room, but the baby's crying or fussing was too disruptive to my first son at night. My first son stopped napping around the time the baby was born. I know other tandem nursing mothers (all met at La Leche League meetings) who all snuggled in bed together and nursed both to sleep either at the same time or separately. You'll just have to experiment to see what works for your family.
"Adventures in Tandem Nursing" by Hilary Flower is a great book to read. It will certainly give you confidence and help you trouble shoot any problems. I know that I had some plugged ducts while tandem nursing and anytime I got that I just had my toddler nurse extra to help clear it up.
My older son is so nurturing and maybe it's because he learned that with me. At 4 now he'll tandem nurse a stuffed animal and a rubber snake...too funny...but so beautiful to see him being compassionate and gentle. Perhaps he'd still be this way without extended nursing. I have no way of knowing, but I have no regrets about those early months of intensive nursing of both of my boys.
Definitely check out a LLL meeting. The one in Evanston has a few tandem nursing mothers. I've since left the Chicago area, but you're welcome to private message me if you want to chat more about nursing.
Good luck to you and congrats!!
J.