+++++ on the Wheels
They feel lighter than they are (rotational mass)

Omni Cassette, 100g or so, great value, better than scram
Buy a second hand crankset with BB save 300g, even FSA SLK that is a couple of years old will be fine, but off ebay qnd do some research (one of my bikes has a Deda D-power (no - you haven't heard of it!) $200 for 560 grams plus a old fashioned ISIS BB (80+g Tokin)
Your chain is fine, carbon bars from a Williams or someone like that save 100g

Not tough at all, just eat less. You'll lose weight and save money at the same time.

Don't worry I'm drinking more to avoid the food

Not doing well finding cranks, so far they're pretty expensive or ISIS which I'm not too fused with hmmm! FSA seem very unpopular and lightning don't seem to be in the Uk.

Continental GP4000's tyres - 205g each lighter thasn what you have. Even foilding gator skins are lighter than what you have.
conti Race 28 supersonic inner tube - 50g each.

As for rims I would build with Stan alpha if the budget allows or with DT Swiss RR415 is you needed a cheaper rim. The Kinlin rims while more aero are heavier so you have a trade off. Weight loss at the tyre/rim is worth much more than weight loss from lacl of spokes or at the hub. A miche cassette is 250g which is lighter than what you have.

_________________
www.thecycleclinic.co.uk

An alternative view:

Since money is tight I would adopt a different approach. Ride the bike and save the money. When something wears out, if it is a wear item, replace it with an Ultegra level part. If it's a non wear item get the Dura Ace or boutique part. Keeping the bike running well is what you need to prioritise. If you compare my wife's bike built by Condor with other bike shops' efforts, you soon realise that the mechanic has a big influence. Although her bike is mid-range, the cabling and bar tape is perfect, the brakes are smooth and shifting works perfectly in all gears. Thus it's nicer to ride than a much more expensive but badly set up bike.

When i used to race a lot (i.e. 5-10x more miles than now, but similar level of maintenance time spent), I used to find that pieces would wear out very quickly. Only brake calipers, stems and front derailleurs seemed to last more than 2 or 3 seasons. And I used to win races on a bike which I'd now consider marginal for riding to the shops, so it's not about the bike.

As for immediate priorities, I would start by ensuring the bike fits properly and that the contact points are the ones which fit / you like. Put good tyres and latex or Supersonic tubes in, then leave it at that. Avoid the lightweight brakes suggested. Downhill Dura Ace (or any decent groupset) brakes will allow more confident descending and faster braking so you easily save more time than you lost on the way up.

Got a DA 7900 crankset and BB on the way

I like doing all the work myself after building an MTB ages ago from scratch. Agreed on the bike fit, this is why I'm paused on bar and stem. Not sure I like the bars much so far as you can't reach the brakes easily on the drops.

I started from scratch but had the same type of budget in mind. I built a set of Kinlin XR-200 rims with Bike Hub Store hubs, Revolution spokes and alloy nipples. Total weight is only 1265g with Veloplugs for under $250! If you need beefier wheels you can go XR-270 or XR-200 with more spokes. They will still end up weighing less than anything in that price range. As suggested in this thread I also went with ISIS because there are many inexpensive and light options. For just over $50 I got an FSA K-Force carbon crank and its only 525g with 53:39 rings. The complete crankset with BB & bolts was 688g for about $105.

See my complete build here:
http://weightweenies.starbike.com/forum/viewtopic.php?f=10&t=93970&start=0

Great job on the bike, that's a cool build

Here's my wheel choice so far as I'm in the UK.... What do you think, all of this stuff seems very well reviewed?

NOVATEC A291SB / F482SB Road Bike Bicycle Hubs 245g 75g
20 \ 24 - available from ebay - Circa £80

Rims - not sure yet but probably one from Halo or IRD (claims are that Kinlin make them all)
Halo Mercury 465grams aero 30mm deep
Circa £80 for two rims

Spokes - CX Sapim?? Not sure yet circa £90 for 20 \ 28 wheel build. Seems expensive but they are areo.

Have you considered Sapim Laser spokes instead? Weight is similar but they are cheaper. However, they are not a bladed spoke like the CX Ray.

As above same weight, 1/3 price and the amount of spoke that "see's" the wind is only marginally more