You can cause vaporization of the MeOH component of the mixture by raising the temp over 150 degrees, the higher you raise the temp the quicker the vaporization will occur.

By leaving that valve open during heating you are providing an escape route for the vapors you are trying to capture. Close the vent. You want all vapor outflow to pass thru your condensor. In theory the open outflow thru the condensor should prevent excessive pressure buildup; however, many moonshiners have been killed by exploding stills. You can close the vent off by installing a pressure relief valve and alleviate that potential.
If the drum you are using as a boiling chamber is a standard 55 gal or similar, you can get a good idea of the temp of the contents by externally measuring the temp of the drum at a point remote from the heat source.
The concept of a "Nitrogen blanket" for saftey is good but it doesn't require over pressure, before you start just fill the headspace with N2 that will drive off any O2 and keep a fire from happening.