That sounds incredibly complicated, best of luck 

Not exactly. The most complicated part is the inverter. I'm probably way in over my head with this

Now on 50 Hz this where I can see thing go wrong esp with magnetic rapid start and CWA ballast that current will go other way with those series to lamp cap set up.  So that means getting your current meter out adjusting your CWA cap to run your lamp correctly on 277 volt tapping
On hid ballast. Electronic ballast there rated 120 to 277 volt 50 / 60 hz.

Now and then on Ebay u can find 50 hz US made rapid start ballast.

I was going to try and get some Quickstart gear from the UK. The problem with the CWA gear is that if I have to change the caps you can only get so many different values. Gets real irritating if you need to change the value and it is miles away from any pre-made values. Good thing about coils is you can take off a few turns or add some in, no problem but capacitors ... eh that's a different story

That's why it's a good idea to generate exactly what the lamp and ballast require. I could probably run the one I have here on 240V using the 277V tap, but it's easier to do it the way I've done it for me and give the thing what it wants (wish someone would do that for me and give me loads of money  )

Capacitors I use are standard motor run caps for electric motors.   Here un the US  it goes 2.5, 3, 4,5, 7.5, 10, 12.5, 15, 17.5 and 20, 25, 30.  Rated for 440 volts

 I do can tell u this if you want to run 800 mA 110 watt HO
On 125 watt pop pack u just need reduce it to next lower value like 6 uF.  On 50 Hz

  But far a running 277 volt CWA
  It will work on 50 Hz but current underdrive
  the lamps.  U might have to increase it by one or two points in uF to bring the lamp current up,  the cap keep current constant to the load.

I remember one austrailan bloke bought a 277 volt rapid start and the lamps were under driven, and it did not incure at time cap is the problem here.

@Sox 35 yes i like your inverter set up for US voltage
It makes things lot easier to enjoy US lighting esp the HPS lamps as there not very many options in ballast choices.  Apart from using 40
Watt 2 ft fluorescent chokes and ignitor for US 35 watt HPS that about it. As american HPS ballast for wattages
35 to 150 watts runs 52-55 arc volts.

Low arc voltage lamps are not a problem, just build up the required current with FL ballasts in parallel. 18W T8 and 4/6/8 and PL-S ballasts all can handle the low arc voltage lamps and are convenient building blocks at 370mA and 160..180mA steps respectively

Same with capacitors...

Low arc voltage lamps are not a problem, just build up the required current...

Not true with lamps, where the arc voltage is dictated by a saturated vapor operated at high temperature (with tight thermal balance; mainly HPS).
These tend to rely on the sloped ballast load characgeristic (increasing arc voltage making the arc current lower and vice versa) to combat the inherent thermal instability (higher temperature causes higher pressure, that causes higher arc voltage and that cause higher dissipated power, increasing the temperature further - so quite strong positive feedback; the sloped ballast characteristic makes the current lower at higher arc voltage, preventing the power from rising that much).
Using inductor ballast from high voltage supply will make the current way less dependent on the arc voltage, so the positive thermal feedback could easily become strong enough to cause a thermal runaway either to way higher temperature/pressure than designed (so damage the lamp) or cause cycling (if really too excessive).