Checked in on a Sunday and found plenty of parking in front of the building. Along the side (9th Street) and directly in front of the building, you can find untimed parking. If you're lucky enough to score a spot, you don't need to worry about meters. Keep an eye out for signage. Download the Parkmobile app to easily pay for parking. You cannot extend the parking time when it expires, you'll have to move your car to another parking zone. I found this was true with the few metered spots around the rest of the DC area too.
The 2-bedroom unit was clean and had enough space for myself and my three children. Check-in was super easy. The info to enter was in the app. We encountered a few of the cleaning staff while heading in and out of the building who seemed really sweet. They all had smiles and greeted us when they caught sight of us. The unit had everything a nice hotel provides and more. I even enjoyed the coffee, which is a rarity. I normally opted for the grounds I always bring with me.
This is a lower unit, so bright, natural lighting is sparse. Don't expect to look out the windows expecting to see the rest of the world outside bathing in sunlight. Didn't bother us, but it might bother some. Plenty of places to eat within a few minutes walk. We used Postmates for quick food delivery and contemplated groceries with them as well, but the drive to Trader Joe's was an easy and short one.
We spent 3 nights at the Callisto and it was definitely a pleasant stay. I would've loved to stay longer if possible. Will absolutely look into this location again for our next trip to DC.