Several strange phenomenon when magnetron interacts with light bulbs Is this video real or is it a hoax? What physics is going on here?
https://youtu.be/POGSEG20hkg
In the video, there appears to be a magnetron set up, and someone is using fluorescent light bulbs and potatoes to play with it.
00:18 - Eighteen seconds into the video, a fluorescent light bulb seems to turn on when the magnetron touches the glass of the bulb.
What causes the bulb to illuminate?
00:28 - At the twenty-eight seconds in, the antenna on the magnetron acts like a candle flame. is this an ordinary flame or some physical effect of the microwaves?
01:05 - One minute and five seconds in, a hollow glass tube, possibly a double ended high power bulb, is placed close to the antenna and only lights up after an initial spark at one end. What extra effect does the initial spark have that makes it light up?
 A: 
00:18 - Eighteen seconds into the video a fluorescent light bulb is caused to illuminate when the antenna touches the glass of the bulb. What causes the bulb to illuminate?

Fluorescent bulbs are filled with a gas that lights up when current (energy) is applied to them. 
From Wikipedia:

"An electric current in the gas excites mercury vapor which produces short-wave ultraviolet light that then causes a phosphor coating on the inside of the lamp to glow."

Since the magnetron is a high-intensity source of microwaves, what's happening is simply the microwaves exciting the phosphor coating instead of an electrical current exciting the gas which excites the phosphor coating.
Note that in both excitation pathways, the phosphor coating is excited by high-energy photons.
_

00:28 - At the twenty-eight seconds in the antenna acts like a candle flame, is this an ordinary flame or a physical effect?

Well, microwaves have been known to mess with flames before, but it's my own opinion that things tend to catch on fire when you provide them with oxygen and dangerous amounts of energy.
In all seriousness, though, I'd guess that there were flammable materials on the antenna. (Oil from handling it, a bit of fluff, etc. And later, potato-residue.) 
Another possibility is that the solder flux or resin in the joint holding the wire to the antenna may have gotten hot enough to boil off and burn.
_

01:05 - One minute and five seconds in a hollow glass tube (possibly a double ended high power bulb) close to the antenna only lights up after an initial spark at one end. What extra effect does the initial spark have to cause the illumination?

I'm not entirely sure. He seemed to use some sort of hand-operated sparkplug, so my guess is that he was using a handheld piezo igniter.
If it was a high-power bulb, it may have required a "jump start" to turn on, and the igniter provided just enough current to do it.
_
The last thing I'll say, is please don't try and do that at home. You'll notice he put a microwave guard around the antenna to limit the exposed volume, but the whole thing was still just a bad idea. That's not the sort of thing you do in your living room (fire risks, pets, no safety protocols, etc.).
I just about quit watching when he was microwaving his hand (he did this periodically), and again when he removed the microwave shield (~2:18).
A: 1)
Do you - in principle - know how these Gas-discharge lamps work? You can archive the same effect with these "plasma balls" and such lamps. The gas atoms/molecules inside the lamp get exited through collisions with ions, which are accelerated by the electro-magnetic field, which is applied from the magnetron
2)
A flame is a physical effect, isn't it? It's more or less the same principle as in 1). The gas (air) around the "wick" gets excited and will emit radiation (heat via infrared, visible light) during the de-excitation. This emitted radiation/light is what you perceive as the flame.
3)
Not 100% sure, but it appears to me that this device is some kind of ion-beam, which might need the electric discharge at one end get the ions going? If you watch closely, you can see this string-like structure of the glowing part, which aligns itself towards the antenna and rips off when moved too far away from it.
So, to answer your main question. No, it's not a hoax
A: not sure what the gas is but its same as your local neon signs there is nothing special about what he is up to this is just exciting argon rayon neon gasses and the like with a high frequency electromagnetic field. could be low frequency not my area of knowledge as to the wavelength but the basic principles are not to obscure its a field interaction with the gasses in the tube.   
