My suggestion is to add some height at the corner of the house. While the red leaf maple is nice right now, it is only going to grow much wider and will not be appropriate for the site. I's say transplant the maple so that it is out in the open with no structures around it. I would also add some plants that will cascade down the stone wall. You would need to do some research to find what would work for your zone and light requirements.

Slug bait is your friend! Unless you have dogs, sprinkle it in a circle around your hostas. The giant ones take a few years to reach maturity, but they would work well in your situation. Choose slug resistant varieties.

Depending on your zone, azaleas might also work.

Speaking of balance your house has a geometrically symmetric facade. This means that in order to appear coordinated with the house the plantings in front of it should also be formally balanced, with the bed on the left and the bed on the right having the same plants and plant placement. So instead of what is there now the bed to the right would have a matching maple of the same variety and size in the center, and so on.

It would also have been better if the retaining wall had been built to have a square corner to go with the consistently rectilinear pattern of the house. However you are of course not going to tear the wall out now.

>I'm trying to come up with a design that doesn't overpower it<

Yes: weeping lace-leaf maples can often look uncomfortable with anything around them that is more assertive than something like a low, fine-textured evergreen ground-cover. So that already in the scheme shown here that yellowish shrub in particular is crowding the tree both visually and physically.