Pressure gauge concern
Your concern over damaging the pressure gauge during ignition and subsequent burn can easily be mitigated: Simple place an isolation valve between the gauge and the manifold; Leave it open (till just before) ignition so you can read the pressure at the time of (or just before) ignition. Close it @ ignition time (or just before) so you can leave the pump running and sucking but protect your gauge. The pump should be fine - in particular if you use the cold trap as suggested.