Hello Matt

You could use methanol, but I did mean methylated spirits because it is not poisonous
If the purity of the KOH is not on the container I would assume it is 90%
If you mean NaOH I would assume 100%
The temperature is not critical. Make sure everything remains liquid and does not boil.

For the easiest method of making your first few mini batches of biodiesel you can not beat the World Famous Dr Pepper Technique (Pat Pend)