3M NaOH/ethanol means making a solution of 3M NaOH with ethanol as the solvent, not water. So, you cannot use your 5M stock of aqueous NaOH to make the 3M ethanolic NaOH.
Yes, absolute ethanol means 100% ethanol (200 proof). You wouldn't associate a concentration with absolute ethanol because its not a solution. In the same way, you don't normally say that pure water is a ~55M solution of H2O.