The metallic taste is, I think, dysgeusia and it is not from the drug lingering in the mouth. More like an effect on the brain, so yeah that lasts as long as the general effect of the drug last corresponding to the levels of it in your blood.
The munchies from trazodone are like those from mirtazapine well-reported, it seems to be a result of 5-HT2C antagonism (an effect on one of the serotonin receptor subtypes). That effect is a little different from getting munchies from any GABAergic, which is probably more a result of GABA/glutamate effects on hypothalamic neurons.
Don't know what to make of that merry-go-round effect but it sounds unpleasant to say the least. I have used mirtazapine in the past and yes I have had some weird nights on it. Unfortunately it did not really help me go to sleep.
Neither zopiclone nor zolpidem are really suitable for treating insomnia longer than about a month, no different from benzo's in that respect. But if you have problems with arousal during sleep zopiclone is better than zolpidem because it acts longer. If not, zolpidem has the advantage of not really usually producing dysgeusia (the metallic taste effect) and the effect being relatively gone / ended come morning.
I *might* try a significant dose of zopiclone tonight, I need to correct my rhythm... it may be an opportunity to briefly check out the hallucinatory effects.