That would be tricky to estimate. First of all you have a tolerance, so if you're taking 30mg, this would need to be in addition to that. As mirtazapine has a fairly strong effect of raising the heart rate, as an alpha-2 antagonist, you need to make sure you don't take too much, as it would not be comfortable.
I would guess that 45mg would be adequate for non-tolerant people. If you were tolerant to 45mg by prescription, I'd say 90mg. The best way to know is to see how much you can take in one dose, although remember that your tolerance needs 2 weeks to reset after this. It's safe up to about 75mg in new users, and after that its seizure-inducing potential may become a problem even for non-epileptics. The cardiac effects would also be strong. They prescribe in doses from 15-45mg, occasionally 60mg, so that should give you an idea. Larger doses are pretty safe but probably would not be desirable.
Please remember this is mostly conjecture, so it's important to test at least once yourself.
Mirtazapine's antiemetic effect is roughly the same affinity as its antidepressant effect at other serotonin receptors, so if you notice a mood lift, and increased hunger, then you can know it's doing the rest. It probably works just fine at the high end of prescribed doses. It works through the same receptors that hospital antiemetics do for chemo, post-anaesthesia, etc.
Important to say: mirtazapine would not keep you asleep during a chloroquinine overdose! It has zero anaesthetic effect, and not even a true sedative effect except as an antihistamine. If there is pain, you will wake straight up, and you will not be calm. You would want to involve one of the following: barbiturate, opioid, or NMDA antagonist at the very least. Mirtazapine increases heart rate and function so this may be a good or bad thing for the overdose. I'm not familiar with how exactly this chemical kills you, what the timeline is like, what the experience is like, but that's what I know about mirtazapine. From what I've read about chloroquinine so far, it's not something I'd choose to die from. Looks pretty horrid, unless you're on very strong drugs beforehand.
You can know that mirtazapine has been absorbed by paying attention to the changes you feel. Sleepiness (which you'll have to fight viciously), dry mouth, hunger, racing heart, mood lift - if all or most of these are present, then it's in your bloodstream and absorbing further. Normally about an hour to absorb, going on past experience, but I haven't looked up its exact pharmacokinetics. You'd want to stay awake as long as you can before you take this chloroquinine stuff, then you'll be woken up when you have a heart attack or whatever this stuff does.
