Not the arc. The arc is at hundreds of kilohertz and mostly travels on the surface, which is why people take hits from streamers and are startled rather than dead. The things on this page are at DC or at mains frequency, they are inside the cabinet, and they do not announce themselves.
The bus bank
Thousands of microfarads at three hundred to six hundred and fifty volts. That is a lethal store, and it does not go away when you switch off.
Indication, and its limits. A bright LED with a dropper resistor tells you the bank is up and bleeds it slowly at the same time. A neon is a useful backup.
Precharge, separately, is about protecting the machine rather than you: a cold bank at switch-on is a short circuit across the mains. A resistor in the AC line before the rectifier, shorted by a relay after a few seconds. And note that a doubler charges roughly twice as slowly, so a delay that was right for a plain rectifier is not right for it.
The frame under the primary
A metal frame under the primary is a one-turn secondary of that primary.
The cure is to break the loop: nylon bushes, washers and Kapton, so that each upper rail is grounded at one end only, and the strike rail taken to RF ground on its own wire rather than through the frame. The numbers are in three grounds and a shorted turn.
The secondary's ground
A counterpoise instead, and a short lead to it, which is its own piece.
The current transformer nobody thinks about
The tank, while the coil is off
The tank capacitor sits in a resonant circuit that has been at kilovolts. It does not have a bleeder in most designs because a bleeder across it would spoil the tank. Treat it as charged, short it deliberately, and do it with something insulated.
And the thing that catches people who know all this
The bench, not the coil. The measurement setup is where most equipment and a fair number of people get hurt, because a scope's ground is bonded to mains earth and a coil's power section is not. Scoping one without killing anything is a separate page and it is worth reading before the first power-up rather than after.
This page is a floor, not a safety course. The safety guide is the site's own, and none of it substitutes for the habit of assuming every capacitor in the cabinet is charged until you have personally shorted it.