I'm a new conure owner, and I've noticed that a conure is a lot like a pet dog and a pet cat and a needy roommate all mixed in one.
She is loud, messy, cuddly, intrusive, moody, intelligent, cute as a button, and unlike any other pet I've ever owned.
It's good you joined this forum and tried to find out more info before actually getting one.
I'm guilty to say I did very little research before bringing home Kiwi, she was actually an impulse buy (horror). And it was a bumpy start because of that.
I don't have much advise for you but that you are doing the right thing, do a whole lot of research so you are as prepared as you can be. If you can get one that has already been hand-tamed, and maybe started on basic training. I think that makes a huge difference especially for a new bird owner.
You will definitely need a big cage - one of those wide and tall ones on wheels with 5/8" or smaller bar spacing. They move around a lot and like to do gymnastics. Get a cage with horizontal bars so they can climb around. You'll need a whole lot of toys and rotate them every two days to keep things fun and interesting!
As for diet, I feed Kiwi harrisons pellets + roudybush pellets all day, and for breakfast and dinner a small amount of mashed up veggies, cooked rice, pasta and squash. She also loves fruits but I give a small amount only every other dinner because they are sugary. Fresh water every day, but I'm sure you know that ^.^ No avocados, caffeine, chocolate, sugary and salty stuff, fruit pits, peanuts.
Spend as much as you can with them..do a little bit of training but also let them be involved in everything you do. Kiwi loves hanging out with me even if I'm doing boring stuff like laundry.
As for diseases I'm not too sure on that, but I'm sure there are lots of posts here about that. The main no no I hear is no air fresheners, no candles, nothing aerosol, pretty much nothing that can contaminate their small sensitive lungs. Also no Teflon pots and pans. I also read that human saliva is dangerous, so no sharing food/water. I am guilty of giving her kisses though sometimes...i can't resist...too cute 0.0
Also be prepared for vet visits. Not just when she's sick, but at the very beginning when you take her home, as well as yearly checkups, like you'd do with any other dependent.
Whew..as you can see it's a WHOLE lot of work. You will lose a lot of the free time you thought you had, and then some. It's a good thing to think about, before committing. It's a lifestyle change.
Sometimes if you can't get all the answers in your post, you can do a search in this forum and most likely you will get the advice from older posts. There's TONS of great advice all over this forum.
Good luck!! ^.^