Damn, all this sounded like a really good idea last night, but now it is starting to look a bit expensive. I just payed £1500 for a uk visa application, so "just" £1k is looking pretty good for a pc.
Then drop the SSD, drop the CPU cooler, fall back to a 7850, and keep the CPU at stock for a while. Do keep a decent power supply and case for later.
Don't rush it. Give it another week to mull around. Deals come and go.
Is the extra cost for a modular power supply worth it?
It's mainly practicality and looks. I've built with modular and non modular just fine. You have more cables to hide.
£360 for a GTX 670 is double that of a 7850 at £180. I'm trying to convince myself that it is worth it, but it will probably be better to get the 7850 now and then in a year or two, buy another card (or maybe another 7850 for crossfire).
Yes perfectly adequate. I run on a 6950 and don't see the need to upgrade (apart from money burning a hole in my pocket). I wouldn't bother with crossfire. Better to upgrade the card imo.
If 60fps in games is enough for me (I'm usually very very happy with 30) then I probably don't need a 120Hz monitor. Right?
It's not just the frame rate, but the input latency. It's like the debate when CRTs were still popular, and LCDs were starting to come to the market. Less latency, less ghosting. For 120Hz display, also 3D, but imo overrated.
In any case, given your budget I wouldn't bother. Stick to a decent monitor, £120-£150. Or use your TV.
Until what time do I have to order today, to get the components by tomorrow? I'm planning an awesome long pc building weekend.
give it 24-48 hours.
EDIT : BTW, don't bother with AMD. It makes far more sense to get a 3570K (or a 2500K if it wasn't so stupidly expensive). It's worth spending a little in that regard. An overclocked 1055T might be ok, but starting from scratch, get the best CPU you can. Or if you can't, replace the 3570K with a i3 which leave you plenty of room for upgrading although imo you're better of getting the i5 straight away.