That Giant will be a touch small- you’d need a large or medium large in a Giant.
I will hold my hands up and say the Carreras second hand are a good deal. Especially since not a lot of them have been used much (bike to work, nice cheap bike during TdF fever, that sort of thing). Gumtree is the best place to look for good deals on them. The TDF you mention is a great first road bike if you can live with the colour!
STI levers refer to integrated brake/gear levers- while they weren’t the best on MTBs they are really a necessity on a road bike these days as taking your hands off the bar and reaching down to change gear at 40mph going down a hill is absolutely chuffing terrifying.