Opinions on Vacuum pumps for purging

Hey guys!

Getting ready to blast most of my crop for the first time and trying to get all my parts in order. I've been doing my homework and have the vac chamber and heating pad lined up, but have been trying to figure out pumps and have seen a mix of feedback in very few places, so was hoping some people could shed light on a couple important factors.

My first hold up is a 1 stage versus a two stage vacuum pump. I see some people saying with stage 1 you'll be fine, but it sounds like a two stage is more desirable as it draws out extra air? Can anyone speak from experience? I'm also blasting at about 5000 feet so I'm not sure if that's a factor that should effect my decision as well? Obviously a 1 stage would save me a bit of money, but will they purge in similar timelines, or any negative effect to the one stage versus the two?

My second hangup in choosing an affordable pump is I've also read that oilless pumps are preferred? Can anyone speak to their experiences with a oil based pump vs without? I've read some of the vacuum pump oil can end up back in your product.

Appreciate the feedback from y'all!

I use an oiled, 2stage and it works just fine. The two stage isn't that much more either. No oil will end up in your end product either. Just ace the pump away from the chamber and draw the exhaust away from the work area.
Their also a handy and fun thing to have around.
As to the altitude, I am not sure. But if you moved this thread to the concentrate and extraction it would be easier to find an answer from someone who would know.
Good luck friend! (And go build a vacuum canon!)

Realized I'm a stoner posting in the wrong place way after the fact