Some people would say that the comedown from MDMA is much less severe than that of amphetamines. I sure would, even though I generally don't have a hard time with meth.
I mean, MDMA does have methamphetamine right there in the name, but its main effects are through an entirely different serotonin transmitter system.
Meanwhile, methylphenidate blocks dopamine reuptake. Amphetamine does too, after it's forced a bunch to be released. Those two do work on the same transmitter system. And if you think your depressed mood is due to a med that isn't working, quit the med, don't add new ones. (But if you do, try to take them as prescribed.)
Clonidine doesn't have to build up in your system, or take a month to become effective, as far as I know (takes a little time). It is not a monoamine reuptake inhibitor. The advantage is it's NOT stimulating, and doesn't involve dopamine and the same addiction risk. And it would wash out of you quickly. It's meant to treat blood pressure; I think ADHD and depression are off-label most everywhere.
Beta blockers are given for anxiety, to help with physical sensations like a fast pulse, wouldn't work for you with amph use.
I'm on sertraline again, and know exactly what you mean by dulled emotions. But your stated priorities sound more like you want to be able to take MDMA on the regular, along with LSD and rec. use of prescription amphetamine. It's true that mirtazapine has low or no affinity for the serotonin transporter protein, which MDMA needs to work. But it would interfere with all the receptors that the serotonin MDMA releases would target. It also has tight antagonism at the 2A serotonin receptor, which is where LSD and a lot of psychedelics function (including MDMA). So it would definitely interfere with those drugs. It also has the same effect on alpha receptors as clonidine. And super-potent histamine effects, so it's very drowsy.
Really, you kind of need to decide which is a priority to you, and right now you're siding with recreation across the board. Not that that's wrong, or anything, you just can't treat a mental illness with drugs and not expect problems with recr drugs.