On One Pompino owners...

BB: Miche

Don't. If you must square taper, the Shimano UN55 is better, so is the Token one which PX were clearing out at £10 last time I looked. My first choice for a shopping bike would be the Shimano FC-S500 crank, which comes with a Tiagra BB anyway.

For the wheels, from what I can see the Halo are around £120 all in, so I guess that is your upper wheel budget? In which case you could build a set yourself for a similar price (Mavic A319 ~£50 or KinLin XC-279 ~£70, novatec hubs ~£50, Spokes ~£20 = ~£120-150). At that price the KinLin in 28h would be my choice, assuming you're under 100kg. Plus you save yourself paying for 8 spokes ;)

If you're on a budget my 2p would be to try and source the below parts for free or as little as possible (£2-5) 2nd hand from the forum or ebay. Then "upgrade" them over time (if you need to). They are parts that new will always be at least in the £5-20 bracket, so you can easily save yourself £50.

Stem: ???
Bars: Planet X
Seatpost: Planet X
Saddle: Planet X

Personally I'd go with wider rims and stretch your budget a little to get them, trimming on other areas. Spending a little more now will be cheaper than buying another set later on. Even if you went with H Plus Son archetype (~£50 p/rim) the wheel cost would only jump ~£50 and would give you a lighter wide wheelset.

The Alfine (FC-S500) crank comes in black and bang for your buck is probably the best deal you'll find.