Wow Bamboo I won't ask what you paid for the cage but I hope you got a good deal for all the work you've put into it. That's a pretty daunting task you've done! Hope you're proud, I've surely had projects that I've put 10 hours into to save $20 bucks, I just call it a labor of love. I hope the smell doesn't return once you paint it.
I have a couple suggestions that might help as they've worked for me anyway. Far as accessibility - You could add a large door to the middle level to ease cleaning - I've had cages where there aren't doors where I want them, so I
make them - combination door/ladders. All you need is a small cage you can get cheap or free, and a dremel or power drill with cutting disc and smoothing bit. (you can get a cheap dremel with bits assortment from Canadian Tire or XS Cargo, or just buy some cheap bits for a power drill).
I made the side doors in both the blue cage and the white cage, small cause I just wanted the kids to be able to come and go, but you could make bigger ones for cleaning.
Hope I can make this clear with some pictures as it's really easy but harder to explain, this is a small hole, but the same principal for a huge one..... Cut a hole in the big cage where you want a door (cut out as many bars as you want to make the hole as big as you want - just cut inside the crossbars on the keeper cage and outside the crossbars on the cutup cage).
Use the cutup cage to cut a door out of (I find it does double duty to cut it extra long so it can double as a ladder). Smooth the cut edges. The door doesn't have to fit the hole - as long as it's bigger than the hole it will work just fine. Just measure and pre-plan so you know the new door will be big enough, and align the bars in the right direction so you will be able to fit clip on to hold it closed (you can get clips in all different sizes tho)...
hole cut in cage, door attached & open
door closed
If you can leave 2 bars on the door long enough to fold over you can use them to attach it to the cage - otherwise you can use wire or split rings to attach it.
Far as securing the door shut for day-to-day opening & closing I use 1 or 2 paper clips and have never had an escape, you can use a bunch if you are concerned, they only take a moment to attach or take off...
Not so pretty as an expensive cage but it sure can make a cage perfect for you & your kids. Hope I explained it well, if not and this can help you then you can pm me if you have any questions, I'm no expert but I've had a lot of practice mickey-mouse-ing things on my rat budget, lol.
P.S. Thankyou so much for caring about Mima dog!