Our IRNs are very acrobatic, so swing height doesn't seem to matter- if they want to get to it, they will!
For perch diameter, try 5/8 to one half of an inch. Variety is the spice of live... or however the saying goes, lol.
Apple is great, and will be devoured eagerly (they're flavoured)! Grape vines are fine, and so are citrus branches.
You really do want perches that can be chewed, as birds need to chew! And IRNs are no exception. In fact, most in the genus Psittacula are avid chewers, since in the wild they excavate their own nests in wood. Chewing is a very healthy activity, both mentally and physically, for birds.
Always make sure you wash branches from outside well, with soap and water and rinse thoroughly. You can use a tiny bit of bleach in water if you want, though grapefruit seed extract (GSE) is a more natural way to go. Or even vinegar and water. ^_^
Some bake their branches dry, but it isn't required. But always allow the branches to dry before using them for your bird.
