The liquid I would optimally want to use is 96% EtOH
A couple of questions- Why do you want to use nearly pure ethanol? Why not simply use distilled water?
If it's for storage purposes I can understand your goal, but even then I would ditch the ethanol and instead recommend making a water solution (no alcohol) and then dividing it up into several "aliquots" before freezing them until needed. 100-200 ul aliquots in polypropylene tubes are perfect, use larger aliquots if you share with fellow psychonauts.
These aliquots will be good for 3-4 freeze/thaw cycles if you re-freeze it immediately after drawing your single use out: e.g. you can thaw one and then draw from it, then re-freeze it... and repeat the process at least 2-3 times without losing apparent potency.
Make absolute sure that you pipette the freshly thawed solution up and down several times to make it homogeneous.
96% EtOH... and since I will only ingest 20-40uL (intranasally, probably), it won't burn too bad. Is this correct?
I think it's still a bad idea... That isn't healthy or sustainable.
reformer reports someone as saying that 6-7mg per mL water has been successfully done for the HCl.
That info has since been updated as the poster uses ~8.5 mg/ml for many NBOMe now and has no problems "solving" HCl salts of the 25C, 25D, or 25E at this concentration. 25E (the least soluble in water) takes a bit of uniform agitation (i.e. vortexing) over a few minutes to go into solution, but reasonable room temperature and no heat is required or should be applied.
That info does not recommend going higher concentration than 8.5 mg/ml for 25E, but guesses that 25C will be soluble up to 9-10 mg/ml (no guarantees).
Frankly, it seems that volumes of less than 30 ul don't work well for liquid insufflation. It's suggested to use 20 ul of distilled water to further dilute your "droplet" of 20 ul 25C to a final volume of 40 ul before insufflating the diluted solution. Then you can add larger proportion of 25C and less water in the 40 ul if you want to make the regimen stronger.
a 100ug per 1uL solution (this seems way out but I'm not an expert - reformer points out that its equal to 100mg/mL). Dondante did 50ug per uL.
100ug/ul = 100mg/ml = 100g/l
That is waaay out there. Since a ml weighs but 1 gram, they are proposing 5 and 10% weight per volume solutions which is unreasonable and likely not homogeneous, at least in water or even low-percentage ethanol.
And... There is absolutely no need for it.