I'm not overly conscious of any of my fid's sleeping habits. They're free to do their own thing, as am I. It's winter/early spring here at the moment so I will try to ensure they're covered overnight, but their room has full windows on both sides so they can do as they please a bit in the natural light.
There's not a massive range of cages in NZ, so these are our go to:
http://theparrotplace.co.nz/ppkeri/wp-content/uploads/images/products/p-1913-604-2.jpg
The ringnecks & lovebirds have their feed doors cable tied with alternative food and water containers - they're smart creatures!
Nearly as important as the cage, are bongs/a playstand for around the house, so they have places to be in your company.
Are you getting a newly weaned baby? Find out how much they're handled...IRN's aren't super hands on birds, and if your hoping to harness train etc., having them used to having their wings handled will make a huuuge difference.
They're amazing parrots

But can be very finicky to work with. Have you got a colour in mind?