EDIT: I just wrote this post in one go and now realized it turned out to be a quite long post. Hopefully it will help you though

!
I can see that noone else more knowledgable of ringnecks has responded, but I will try to give you an overview of what happened when we introduced our two parrots!
I think you are familiar with my two parrots, Stitch and Leroy, but just to be sure, Stitch is our first parrot and is a white fronted amazon and weighs in at about 185grams. Leroy is the parrot we got later, because we didnt want Stitch to be alone during the days, and he is a bronze winged pionus with a weight of 230grams. They are roughly the same size, Leroy being a little sturdier built.
When we first started looking for a buddy for Stitch we initially looked for one of the same species, but this proved to be impossible to find. Therefore, we broadened our search for a species that might work with our little guy. After talking to loads of people, both here on the boards, but also breeders, rescues and parrot associations, we decided that a Pionus might work well.
We got Leroy, and he was in a rough condition when he arrived but has since recovered all his flight feathers (they were not clipped but damaged) and is a joy to see him flying around now, more secure than ever. He also was very nervous around us in the beginning, but is now starting to warm towards us =).
Well, to the introduction!
At first we kept Leroy as isolated as possible for 3-4 weeks, during a quarantine period. He was then in a different room, and they didnt even recognize that it might be a bird somewhere else in the house, Leroy because he was nervous, Stitch because he hadnt seen another bird since living with other amazons at the breeder (and we got him at 3 months old, so he basically only knew people rather than birds).
We then decided to move their cages into the same room, first starting at different parts of the room and gradually moved them closer and closer to each other. Both parrots then started to show parallell behaviour, which indicates that they start to accept the other bird as part of a flock, so we thought that the time was ready for a supervised meeting between the two of them.
It didnt go all to well. Both because WE werent prepared how birds interact, but mainly because Stitch didnt know how to be a bird (and we had him for about 6months, imagine how it must be for a parrot that has been alone with humans longer). Stitch was very curious about Leroy and went up to him and decided to say hello the best way he could: by singing opera!
Leroy thought, what the h*ll, and reacted thus with a small attack. Stitch being unprepared for this fled, but then retaliated with chasing Leroy around the whole living room.
I felt like crap afterwards, but with hindsight it wasnt as bad as I thought it would be.
Eventually we put them together again, after much consideration and talks with our breeders (both Stitch's and Leroy's, breeders here arent generally the money crazy obstinate people that you guys from the states tend to describe) and others. We put them into a large aviary cage I built, and they got on very well from the start!
After that we had a period with fighting, and I posted about this on the forums, but again, with hindsight, it wasnt nearly as bad as I thought it was at the time. The fighting passed, and they got on very well, with the occasional quarrel.
After a while I decided I didnt want to risk them living in the same cage any longer, and they now live in a huge cage with a divider(and plexiglass to avoid toes getting bitten). This works great.
At first after the new cage setup, they were so exited to see each other that they could only be out together for like 15-30min, and with supervision, going from preening each other to fighting back and forth.
With slowly getting them used to being out together, they can now be out for 3-5 hours with no problem at all, preening each other, trying to spot other birds through the window or doing other stuff! They are best friends in the world, and when they are let out, they ignore me and my wife for the first 10min or so, just caring about each other, preening away because they've missed the other one so much (even though they are out together every afternoon ^^).
Its a joy to see, and getting a second bird definetely was the right choice. They entertain each other during the day when me and my wife are at work, and have loads of fun together when out when we are home. It has made Stitch a much more confident bird, and Leroy's development has been so rewarding to experience.
Hope it helps somewhat, its only my personal experience to introducing two birds, but it should give you some insight to what it can be like

. Bear in mind that it could easily have gone the other way though, and turned out bad.