First road bike- please help!

If you buy a bike with tektro brakes it's well worth replacing the brake blocks straight away with some swiss stops (my favourite) or Kool stops.  They are so much better than the original ones.  I've also found them to be better than the Shimano supplied pads on their tiagra brakes but others speak highly of the Shimano Ultegra pads.

Once you've done some cycling it  may also be worth replacing the tyres as thats the other point where suppliers cut costs on the lower end bikes.

 All the major brands will have similar offerings that are more or less the same price.

In terms of what is ‘fast’, road bikes are broadly split into two categories: endurance and race. Endurance bikes are more upright and comfort-focused, whereas race bikes are more aggressive and have twitcher handling. As a general statement race bikes are ‘faster’ than endurance bikes, but ultimately you will be fastest on a bike that fits your body (taking into account strength, flexibility etc). Go to a bike shop and get measured up.

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A road bike would certainly be the best option.

In terms of frame material, given your budget, Aluminium is the only sensible option.

At the top end of your budget, you'll get Shimano 105 11 speed, I would recommend 105 as it really is fantastic. If you had a lower groupset with fewer speeds you'd end up wanting an upgrade pretty quickly.

In terms of braking, you won't be able to get decent (hydraulic) disc brakes within budget.

The women's specific side of things isn't too well catered for below £1000, unfortunately. Many of the womens specific bikes have downgraded components - this is something my other half had been really annoyed with when she was trying to by her first bike. 

What to look out for is what bikes have downgraded components, many manufacturers use lower spec brakes and chainset to save money. Tektro calliper brakes, in my experience, have the braking power of cheese compared to Shimano brakes! Cheaper cranks weigh a little more. I wouldn't scrimp on brakes, but a little extra weight on crankset isn't too much of an issue.

Trying out a load of bikes is the most important thing.

As others have said, Decathlon offer amazing value. Canyon offer similarly great value, in fact, even better. For £1k, Canyon gives you full 105 (including crankset and brakes) and a women-specific frame https://www.canyon.com/en-gb/road/endurace/endurace-wmn-al-7-0.html

Longer term, for TT/ triathlons, stick a pair of clip-on aero bars onto the bike to make the biggest difference!

You don't see many people training on their tri-bikes so a road bike is the way to go.

Women-specific bikes may come with narrower bars and a different saddle but that will be the only difference and at 5'6" you may have a wider choice. That tends to be a small to medium men's size but there's a lot of variation. A lot depends on whether your height is in your legs or your torso. 

A lot also depends on how low/flat you can tolerate position-wise. This is something you'll adapt to as you get used to road riding so it's tricky.

I'd strongly recommend either finding a friendly local bike shop or going to Evans if there is one near you. Evans offer a 30-day ride and return option, even under C2W. The other option is to join a club and see if anyone will let you try out a bike you're interested in.

The thing with buying a bike is that they're all more or less the same, particularly if you've never ridden a road bike. This means it comes down to practical things like "Am I comfortable?", "Do I have the right gearing?" and emotional things like "It's red, so it's immediately faster, right?" 

Don't get too tied up in specs and brands and materials - find a way to be able to chuck your leg over a few bikes and go from there. If you're doing 50-milers and Tris then more than anything the most important thing is that you're comfortable, and you'll only be able to find that out with a test ride of 10-20 miles. 

At a £1000 there is a ton of choice out there. Personally I'd go with a race-geometry rim-braked aluminium bike. Specialized, Cannondale, Merida, and Giant all have very capable bikes that will come in under the C2W budget. Stay away from discs because of your budget. 

Don't rule out the likes of Decathlon, Planet-X, and Ribble - something like this for example https://www.decathlon.co.uk/ultra-900-af-road-bike-105-id_8377261.html

Hi

Welcome to the roadie gang! If you've not ridden a road bike before, you are in for a pleasant surprise

There are so many bikes to chose, it's crazy, and you'll get just as many recommendations. I've not long ago got a Specialized Allez Elite, on the cycle to work scheme, and it's right at the limit of what you can get, £999. I think there is a female equivalent? I can highly recommend the bike, I use it for commuting duties as well as weekend rides up to around 80 miles (so far). The bike has been faultless - in my view the very decent frame (which has a lovely paint job, I have the sky blue one, super easy to keep clean!) with good spec of components, nothing cries out to be changed or upgraded. Personally I don't race (well, only myself!), but the general blurb on the bike is that it is suitable for a starter racer. It will also take mudguards and a rack apparently, but I haven't fitted any. I've been riding for many years, and have a few bikes, and this one deffo impresses.

Whatever you get, have fun and enjoy the ride