Wheels (rims) would probably pend on what type of tires you are looking to use (width) and how much clearance your frame has?
Wider rims and the tires bulb out more (wider).
Sure, you state G-One, if you like those i would suggest Hutchinson Overide also, as these two are as close.
Slight benefit to Overide.
Personally i don't think either of them gives confidence if you corner on loose over hard.
Or slippery gravel roads with much loose. The bike tends to go in an S-pattern (a bit dramatised).
So for gravel there are for sure better tires.
What is missing is a pattern that extends a bit to the edges for cornering grip.
What about these rims (i would personally pick these for tires 34-40mm) ?http://www.noxcomposites.com/citico
Light weight 700c alu rimshttp://www.ryde.nl/pulse-comp-disc
Light weight 650B alu rimshttp://www.ryde.nl/trace-22_1
I wouldn't exclude cheaper hubs like Hope RS4 (6 bolt or centerlock)
Also brass nipples so you avoid corrosion!!
Aero spokes are stiffer than round spokes, so Sapim CX-Ray or DT Swiss Aerolite would be great.
I run 650B, Ryde Trace 22, black rims with white logos (stickers), black Hope RS4 centerlock, 28 spokes, black brass nipples, black Sapim CX-Ray on non drive side, white DT Swiss on drive side.
Works great and looks awesome!
Handlebar, well, that is what you like in terms of angle?
If you like the round bend, you have Ritchey WCS EvoMax, or Neomax (very similar design) with a 12 degree flare.
You still have shifters in a normal position, which you frankly have not with some of the wilder flared bars.
Or you got the Salsa bars which have more drop and reach, but also available in different flares.
Lastly, Eastons AX series gravel bars (carbon or alu).
Stem, what you like in terms of angle, length and style (weight ofcourse).
What about MTB pedals and shoes?
I prefer that as it is much easier to walk in if you'd need.
Look and Time/ Mavic has excellent MTB pedals.
I run Mavic Crossmax SL Pro (excellent) + Giro VR-90 / Nortwave Extreme GTX mtb (winter)
Seatpost, what do you need?
Syntace P6 Hiflex carbon is a good post and most people really like it.
Saddle, your arse and nutsack is the boss here...