I think you have to be honest with yourself about what kind of cycling you are going to do the most.
Sounds as though you have plans to do some longer rides. If you go for one of the off-the-rack "racer boy" bikes you are going to run into some trouble. Most bicycles influenced by racing design will create problems if you want to add mudguards, racks, etc.
For example, ask yourself if the bike you're looking at has eyelets and braze-ons for at least a rear rack and mudguard stays ...
and is there enough clearance for mudguards
under the rear brake bridge and the fork crown. If not, that won't be a good choice for distance riding.
If, on the other hand, you're only planning shorter day rides in good weather, then by all means go for the racing bike.
I second suggestions that you look around for a good used bike. You're likely to get good value for your money, if you shop carefully.
I wouldn't get hung up on "brifters" -- STI or Ergopower -- unless you can afford the higher end stuff (minimum 105 in Shimano, Veloce in Camagnolo) Again, you're more likely to be able to afford this in a used bike.
A less expensive and very dependable alternative can be had in bar-end shifters. These are great for touring and audax. Very dependable. I just came back from a 60km spin on
my bike outfitted with bar-ends and am always reminded how positive and simple the shifting is. I certainly find them no worse than the expensive (£300) and fragile Campagnolo Record Ergopower shifters I have on another bike.
I'm not sure what's widely available in the UK these days. I know when I was a young lad in Wolverhampton, there was no shortage of excellent used bicycles for sale. That's where me and all my riding chums got our first machines.
I did notice the
Decathlon bikes (in those HUGE sports emporiums!) in France, last year, and agree there seemed to be some good value there.
Anyway, good luck on your search. I hope I haven't added to what can be a confusing decision. Remember, in the end it's all about the adventure, not the technology.
Happy trails.