Do I need a tourer or can I get away with a road bike & backpack for a week away?

A good audax bike will do everything you need and more. If the pinarello you linked to above is about your budget then a higer spec audax bike could easily be had second hand. Given how light you are planning on travelling, a carradice would fit the bill as well to carry your stuff.

This. Definitely.

I would (and did) look at Kinesis. They have a good rep, a few on here have used them for racing, very practical.

If you're touring in the summer, you can use 28c without mudgaurds (or maybe clip-on's), plus a rack.

~~A older 105 tripple groupset: ~~

^^ cx is another option. But it sounds like you want a road bike, but also want to do touring this summer... in which case go for the thing you'll get most use from.