years. Probably 5 or more years.
As for vacuum gauges you can find a nice, industrial grade one, liquid filled and everything at amazon for $25 or less
I'm pretty sure you can weld it/bolt it to a small Tee tube piece that fits inside hoses, or find someone who does for the very modest price of two beers lol
As for required vacuum range for the gauge, I say 0 to 1 bar or less?
Any bottles used for vacuum filtration must be rated for vacuum use (at least 25” Hg,0.85 Bar, 12.28 psi) and free from scratches, chip and cracks.
https://tools.thermofisher.com/content/sfs/brochures/Filtration-FAQs-June2013.pdf