Natalie...even if you've owned these birds for years you can still learn. No one is turly an expert
As for your questions I'll try my best to answer
Cage type- As large as you can find with 5/8 or less of bar spacing. I suppose you could go a tad bigger but small is better. Don't want your bird getting it's head stuck in the bars...not a good idea Also, try for a cage with more horizontal bars, they love to climb and vertical bars are harder to keep a grip on.
Food- good tip is if you wont eat it dont feed it to your bird. Find a good pellet mix (Harrison's is probably the best I've found) and give that as the daily food but also mix in about 2 or 3 tablespoons of a decent seed mixture. They have an inate need to crack seeds so please provide thise for them. Try not to give sunflower seeds or safflower (those tiny white seeds in most mixtures) as these are like giving your bird a choice of eating fruits to a snickers bar. Fresh fruits and veggies are a MUST but as Natalie pointed out NO avacado, caffine, chocolate, onion, citrus pips, no apple seeds but the flesh is fine.
Toys- this is what the birds likes. Prinny adores anything with bells that she can just beat the daylights out of. Anything with beads she also loves to play with. She really isn't much of a wood chewer but some are. Buy a varity of toys and change them out every week so your bird doesn't get bored.
Flightsuits- Prinny HATES a flightsuit but I have heard of birds taking to them just fine. Best idea is to start early and be firm but gentle when trying to get your bird used to them. When I take Prinny out and about she is usually inside my overshirt or in her carrier since she will not take to a flight suit.
Poisions- look this up on websites...you will find complete lists everywhere...too many to count!
Keep asking as many questions as you can think of...one of us will have the answer.
Other birds- Please be warned these birds have different personalities and be very VERy careful when introducing to others. Good rule of thumb is never leave them alone by themselves. I have heard of most tolerating other birds but Prinny has never really been around other birds Ask Mazziemom or Neo for these particular answers.
Treats- anything you want to call a treat. Prinny loves spray millet so that's a treat for her. Sometimes I'll give her a few sunflower seeds but those are a special treat. Fruits and veggies can be used for treats...find a food your bird will go crazy for and figure that makes a good treat.
Please ask away...we're just brimming with knowledge and will share willingly
No two IRNs are the same...this is the biggest most important thing you have to remember so not everything here will apply to your bird.
Dani and Prinny