Than you can skip the hollow state part altogether. And any plastic-package parts would screw your vacuum up badly - if it survives sealing and bakeout that is.
That depends. Often vacuum tubes are used with DC (that is a rectifier) in some form though, in which case you can't do this since induction depends on AC. I'm not sure what purpose the article had for a triode though, depending on their application this might work.
But most hollow-state devices run on either DC or pulses, so coupled inductors wouldn't work.