One thing I feel needs pointing out, our Moon is already in an unstable Orbit (some time millions of years from now it's likely going to
impact drift away from Earth), so how exactly did you stabilize the Lunar Orbit?
There's a few different options and I'm curious which you decide to use, the one that comes to my mind is to speed up it's rotation around the Planet, but when combined with the limit of the 27~28 Day Cycle into a 20 Day Cycle, I'm curious just how much closer you moved it if you did increase velocity.
Another facet I don't see covered is the Axis and Rotation, our Moon for example is on equal Axis with us and it's rotation keeps pace with us, this is known as Tidal Lock, one side always faces us and that side never changes unless something else comes along to alter that, does your Moon still have Tidal Lock?
If not that's going to affect Tidal Pull, which affects Weather, Ocean Activity (High/Low Tide, Hurricanes, etc.), Erosion Patterns and Erosion Speed, and also Earthquakes due to the shifting pull on the crusts (in your case, more everything due to increased Activity, it becomes a variable if not Tidal Locked, Constant if it is)
If the rotation is changed, you need to consider how it's changes are going to reflect on the Planet, if it's going with the spin, you have plenty of room to accelerate the Lunar Speeds, as the Planet will have very little Pull on the Moon, where if you are going opposite direction from Planetary Rotation, it's like running your hand across Sandpaper, it's going to grab a lot of velocity in very little time, not as much wiggle room, and generally destabilizes the orbit faster.
You're also going to need to factor in Mass, Gravity is directly proportional to Mass, if you have a huge chunk of Rock, and you move a smaller chunk of Rock next to it, those Rocks want to Smash together, but all the Gravity already affecting them (Earth) is disrupting the Pull between the two and drowning it out (making it heavy, this is how we Weigh it's Mass, which tells us it's gravitational pull), Bigger Earth, closer Moon, just bigger Rocks, it's up to you to decide their Mass though.
If your Earth is raining Diamonds, I'd give it about three years before it's raining a Moon, that 10km Radius in the Roche Limit is with 1.0 Gravity, which is Earth (our Baseline), more Mass, larger Radius, Jupiter for example, it actually does rain Diamonds on the Surface, the Surface it's self is likely smaller than our Moon though, combined with the fact that we've never measured the Surface Depth beneath that Cloud layer (not for a lack of trying), you can imagine the Roche Limit on it.
Also, the Magnetic Field is generated by our Planet's Core, one currently active theory is there's a gigantic electromagnetic Storm on the Core's surface because the Iron is under so much intense pressure that it's crystalized into Iron Crystals, which in turn gives off a piezo-electric Discharge (proportional to it's size), which reacts with the various Cosmic effects in our localized band of orbit (Cosmic Radiation and whatnot) to generate our Massive magnetic field which keeps us safe and allows Compasses to function.