In terms of your GPU I think your main options are the HD7770 (which will set you back around £90) or if you are willing to spend a little
more, the 650TI 1GB models (which will cost around £120, maybe a little bit less if you shop around). I'd say the real "hey I got some decent graphics action going on here" feeling starts at the 7850 (preferably 2GB) but then you'd be looking at a price-tag around £140-£160. BTW this pricing is based on some searching on scan, but I don't live in the UK so I wouldn't know where to shop around over there. Anyway, prices might differ a little bit.
But here's also another thought: why buy a GPU at all if you do not plan on gaming yet? The 3570K has an integrated hd 4000 chip on board, which will give you very decent performance outside of games. Some searching on Google also tells me that it will to quite well in terms of Photoshop for your wife. If you'd go this way, you'd save £100 which you can then add to your budget for something really nice if you do want to start gaming (for instance a 660TI, 670, 7870 or 7950) eventually.
In terms of your PSU my general feeling is: "if it delivers the power you need, than it's all good". Except when there's real issues like noise or something. In my spare rig I've got a 620 watt PSU from CM and it drives an overclocked i5-750 as well as 2 5850's in crossfire. I'm even using these
kinds of cables. Some would be horrified, but they have served my fine for the past year and a half. I do have an overpriced overkill AX850 in my main rig but this is mostly because you can buy nice cable sets for them so it looks great in my case (and I needed a new PSU because I needed one in my spare rig, so I thought "why not something worth the upgrade"
Anyway, I think the PSU's of your choice will do fine, but you might consider going for a bit more wattage (more than 400, 500 would do) if you do plan on getting a high end graphics card in the future. Of the PSU's you proposed I would probably go with the Silencer MKIII as well because of it's partially modular design (the CM is not modular at all I believe), but I'd go for the 500W myself just to be on the safe side for the future (maybe the 400 will power a nice graphics card as well, but I'd just go the safe route now that you're investing anyway). I did hear that the fan can be a bit noisy at high loads though, just so you know. Overall, I think it's a nice one.
As far as memory goes I think you made a good choice, as long as you can stand the looks on your awesome looking Sabertooth. Timings are great, and you don't really gain significant real-life performance when going with anything above 1600Mhz. The price is also really nice.
Hope this helps!