Generally you purge, vac, then fill WHILE the ENTIRE SYSTEM is still vacced. Do NOT release the vacuum before filling the system. That low side pressure really shouldn't ever go above 100 psi tbh, and that high is really only for when the compressor is not running for an extended period (low and high should equalize). Running, low should be between 45-55, high side pressures between 150-200 at engine idle, 200-300 revved.
Don't fill by pressure - if your system calls for 2.5 pounds of refrigerant, only put in 2.5 pounds (40 ounces, or just over 3 12oz cans). A little less is okay but don't go too low or the evaporator will freeze.
And yes that Schrader valve on the condenser is for the 88-95 (TBI trucks) high pressure switch. It was moved to the line just above the compressor on later models, but replacement condensers are pretty universal. My new parallel flow condenser on my 97 has one there too, I just capped it.