Okay, I don't think you have any problem here at all, not with the urate anyway. Their urates do tend to be hard and even chalky at times, and if there is excess water in his bowel movements then he's definitely not dehydrated at all. Most dragons don't drink any water at all, just as they don't in the wild (there is no standing water in the Australian Desert to drink). Most dragons have no concept of what "water" or "standing water" actually even is. They get all the
hydration they need from the live insects and fresh greens/veggies.
That being said, It's alarming to me that you've not been giving him much calcium powder at all, this is a big no-no. Regardless of his age (I don't know how old he is) he needs to get calcium 5 times a week and a multivitamin 3 times a week. A "hard" or "chalky" urate is not at all a sign of "too much calcium", I don't know who told you that but they're wrong. If any excess calcium passes in their urates it tints the urate a pinkish color, it has nothing to do with it's hardness. So please, get him back to getting calcium at least 4 times a week as an adult, 5 if he's under 2 years (I still give calcium to my adults 5 times a week anyway) and a multivitamin 3 times a week, as this will without a doubt cause you tremendous issues soon enough.
As far as the black-beard goes, it was probably due to the CHE causing him to be way too hot. He should never need a CHE during the daytime, his bright-white colored basking bulb should be enough to keep his Basking Spot Surface Temp and his Hot Side Ambient Temp within the correct ranges, if it's a bit too low (5-10 degrees too low for either) you can lower the basking bulb towards him, if it's way too low then you need to use a higher wattage of basking bulb. And as far as for nighttime, they actually sleep most soundly if it's cooler, as Cooper said 65 degrees as a low, low 70's as a high for his nighttime sleep. If he's too hot during the night (into the high 70's is too hot at nighttime) then he won't sleep well. So this is most likely why he was black-bearding, and would also actually dehydrate him.
As far as him being dehydrated, the only reason that should happen is #1) His temperatures inside his tank are too high, #2) He's not eating enough live insects and/or fresh greens/veggies (depending on his age). If he was dehydrated the signs are typically #1) Droopy Eyes, #2) An orange tint to his urates, and #3) Very excessive loose skin (not just a few wrinkles). So I don't think he's at all dehydrated, nor was he ever, especially if you were basing that on a "hard urate". The fact that excess fluid is seen in his bowel movements is a very good sign that he's well-
hydrated.
I think he's just fine. A winter slow-down in appetite and a bit more lethargy is perfectly normal, both of mine are doing the same thing right now, it seems particularly harsh right now because it's been so cold. They can sense the drop in barometric pressure outside even if their tanks are warm, so they know it's winter and this causes a normal slow-down in them. It's perfectly normal.
Honestly, it sounds like he's just fine, everything is fine except he needs to be getting regular calcium and multivitamins again starting ASAP. Other than that I don't think you have a problem. If he'll take extra water from a bottle or from dripping it on his snout or from a
bath or however he'll do it that's fine, but don't be alarmed if he won't, most won't. I've yet to have a dragon that will drink any standing water, not from a
bath or a bowl. They will lick it off their snouts, which I do give them at least once a day, but I've yet to have one that was dehydrated, as they get all the
hydration they need from their food. And your boy looks nice and big and healthy. I think he's fine, just get him back on his calcium and multivitamin supplements and he'll be fine.