Welcome!
"Must haves"? Obvously a Air purifier, what paint brands are safe for birds? what did you use as far as perching, toys etc? Love to see pictures of your Bird rooms!
We have 5 cockatiels, a aferican Grey and a cockatoo!
You dont need an air purifier imo, as long as you clean the room thouroughly, and often. There is a debate whether or not a humidifier is beneficial or not, but it makes more trouble than it helps as I see it, and I shower all birds regularly instead.
What you DO need to do though is bird proof the room:
*Make sure there are NO electrical wires that the bird can chew on.
Here's some suggestions:
http://theparrotforum.com/viewtopic.php?f=18&t=10471*Make sure the bird cant fall down behind stuff, and thus get stuck.
*Make sure to proof the window, if necessary with an extra lock or something so that someone doesnt accidently opens it.
*Dont keep things that are dangerous to birds in the room, such as ink pens etc (long list here, use your judgement and ask if you are uncertain.
Paint shouldnt be a problem unless your birds eat the walls, but I would go with a waterbased paint which is allergetically tested, there are such paints out there I believe:). Still, when you paint, move the parrots to another room and make sure to keep a few doors closed between them and the paint while its drying and make sure to thouroughly air the room out afterwards. You can also move them to someone else for a couple of days if you are nervous, but if you do as above, I do not think its necessary.
With perches, you can do pretty much anything

. Thats the fun part.
I built a tree a while back which you can find here (ive since dissambled it though, as they continously started fighting on it

)
http://theparrotforum.com/viewtopic.php?f=9&t=8025&p=58710&hilit=tree#p58710Here's a guide on building regular perches I did a while back:
http://theparrotforum.com/viewtopic.php?f=9&t=9761&p=66638&hilit=tree#p66638Indefine built this a while back, which looks great:
http://theparrotforum.com/viewtopic.php?f=22&t=10923&p=76379&hilit=tree#p76379Mrbowlerhat has built some really nice stuff, see here:
http://theparrotforum.com/viewtopic.php?f=25&t=11431Polarn built a nice tree as well:
http://theparrotforum.com/viewtopic.php?f=9&t=8965&p=61098&hilit=tree#p61098Make sure its all easy to clean.
And lots and lots of toys of course

.
Again, welcome to the forums!