How tall are you? WSD vs unisex is pretty much determined by your proportions. I'd argue, though, if you can get the reach right, who cares what the label says? (My "stable" has one WSD bike and two unisex bikes.) Long legs relative to your height usually means WSD; more even proportions or shorter legs says you should look more closely at unisex. That's a general rule and isn't going to work for everyone. (Arm length, flexibility, all that stuff plays a role.) I believe the WSD FX have step-through frames. Do you want a step-through? How tall are you? If you're under 5'4" (or thereabouts), you might have better luck finding a WSD. If you're over 5'8"-5'9" or so, unisex might be your best bet. (They tend not to make unisex frames in the small sizes, or WSD in the larger sizes.)

Between the 7.2 and 7.3, it really depends. What are the road surfaces like? Will you have to pick up the bike and carry it up stairs? How highly do you prioritize speed? Steel is more comfy (generally), but heavier. Aluminum tends to be lighter but more "buzzy." I think the speed off the mark of the 7.2 will improve as you get used to the bike and as your fitness improves. (Riding a bike outside is very different from spinning classes!) Bear in mind that you'll need lights, fenders and probably a rack and panniers or something similar for groceries. Oh, and probably a new saddle. You don't have to get it all NOW, but bear that in mind as you put your budget together. Is the extra money worth the weight savings and extra speed? Only you can really make that determination.

If you'd like some other suggestions...I don't know what's available in the UK besides the big brands. Besides Trek, take a look at Giant (the Rapid or the Dash are the equivalent of the FX), Specialized (Vita, and I can't remember the name of the unisex version), Fuji (I think they have a UK distributor, but I'm not sure). There's also the Cannondale Quick. If Jamis is available in the UK, take a look at the Coda/Coda Femme. Steel, but very nice bikes. Since you're in the UK, take a look at Charge. You should be able to find them more easily. Take a look at the Grater. (Or Zester, if you can find the 2013 models. They changed all their bike lines for 2014, so I'm still a little unclear as to what's what.)