If you have buns they will not need a ramp unless they are dwarves. I have a mini rex (5-6lb) and a two tier cavy castle (spoiled) with an attached playard. I have no ramps at all. Him and his mate jump from one level to another - it's great exercise for them.
I also hang Parrot toys with big bells on them. My minirex loves to run back and forth to ring the bell.
Another play toy I use is a cardboard cement tube that you can get at home depot. I cut it down to about 3 feet and stuff hay into the middle of it. You can also use this as a bridge from one section of the cage to another (like a loft).
I use wood stove pellets (cheap) for the litterbox with a bit of white paper (cross-cut shredded) on top for fluff. The wood pellets soak up the urine and prevent any smells. The buns like to play with the fluff.
Okay so I added a bit more to the question but I love my buns!