I personally use 90% H20 / 10%EtOH and that works fine for dilution factors. I found mine was a little tough to dissolve in strictly water, so the mixed solvent is your best bet
Personally I would dilute it in a marked container using pipettes so you know you have some degree of accuracy - but it should be ok as long as you're a little analytic about what you're doing
I'd not use methanol to dissolve it in. Ingesting methanol can lead to blindness. I doubt that a dose of nbome dissolved into 1ml of methanol would cause any harm but why take the risk? EtOH is ethanol, or more commonly known as alcohol. To get a 10% ethanol solution in water I'd add 1 part vodka to 3 parts water.