This cage is way too small for a yellow naped Amazon. Rule of thumb is the bigger the better, but MINIMUM would be 36”x24”x48” interior. Please take note that the height of the cage from top to bottom includes legs and you need to look at interior measurements 

Large Actual interior cage dimensions: 30" L X 20" W X 36" H. Cage height with stand: 63" H. Size X-Large Actual interior cage dimensions: 36" L X 24" W X 36" H. Cage height with stand: 66" H.

Yes the grate on the bottom slides right out and is removable for cleaning. And yes absolutely safe as there is a full metal fixed bottom below the cleaning grate tray. Your Conure and my Umbrella Cockatoo can not escape and are safe when the bottom grate tray is removed. And Yes, the bar spacing is 5/8" on the x-large cage. Would make a great cage for your Conure. We have had ours for a few years now and our Cockatoo loves it. The top play area and feeding area with the stainless steel food and water cups (4 total) are also very nice and a great size. I totally recommend the cage and hope I have helped in answering all of your questions.

We have no problem with our large parrot chewing it off.  Holds up very well.

I have the X-large size which is 3ft wide by 2ft across and about 34 inch tall of interior space (not counting the bottom grille and tray). I have 2 cockatiels and this a nice big cage for them. This would also work for a larger parrot. The large size is 30” x 22” and several inches shorter. 

The cage has lots of room for my large parrot Umbrella Cockatoo to exercise inside and a play area on top. It is very roomy.

i would say not really. i have the medium, which is super roomy for my pineapple conure, but by the time you add toys and perches the inside space gets eaten up. my guy loves to climb in and around, but we are harness training for flight outside and plan on letting him be flighted inside the house when supervised! I'm not sure the large or xl would offer enough space for actual flight either.