A quick Google suggests that you could get that particular bike significantly cheaper elsewhere, but there's a lot to be said for buying from a local bike shop (LBS) if they're helpful and supportive. Bear in mind though that most shops will only stock a few brands out of the many that are available so will be limited in what they can offer.
I'd suggest, as others have said already, that you ought to try and test ride a few bikes before you buy. Find out what feels right for you - it's surprising what a difference small adjustments to sizing and positioning can make and a good LBS should be happy to alter things around for you and let you try a few different makes and models. You and your friend are unlikely to be exactly the same size, so what suits you may not suit your friend (and vice-versa of course).
Even more fundamentally, do you want a drop handled 'racing' bike, or flat bars? Or even a mountain bike? You say in your OP that you will be sticking predominantly to roads - does that mean some of your riding will be off-road? If so then you need to think about how suitable some of the bikes you've been pointed towards will be.
It does sound as if you have a few quid to play with, but I'd echo some of the other comments about not spending too much on your first bike. I'd guess that most people who 'get into' cycling change their bike (finances permitting) within a year or two, as they become more aware of what they want from their bike.
Re the extras - you can easily spend hundreds on specialist clothing, locks, helmets, lights...the list is almost endless, it's a whole new consumer experience
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But you certainly don't
need all that stuff. Personally I'd buy the minimum* to start with, then buy what you need when you know what you need, if that makes sense?
*My personal minimum would be a helmet, gloves, basic tool kit (enough to repair a puncture and a couple of allen keys to tighten things up if they come loose) and a water bottle. And probably padded shorts. Add a lock if you're planning to leave your bike unattended. You may not look the part wearing tracky bottoms, trainers and a t-shirt, but does it really matter? If it does and money's no object, go for as much kit as you want!
Most importantly - don't forget to get out and ride and ENJOY it
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