In reply to maybe_si:
I have nothing to offer about gravel.
as far as a road bike is concerned- if you’re not into flat-out speed and want to enjoy road riding, then with that budget I’d start with a pair of hand built wheels on Chris King hubs. The latter will last for years and years and they will be comfortable to ride.
then decide what sort of frame you want. Carbon, Ti, steel, stainless or alloy. I have one carbon aero, one carbon round tubes, and one stainless. They’re all lovely to ride, but all different. All are quick. The round tube bikes are both head turners. The aero one just looks like a plastic coat hanger, like all of its ilk. The stainless one will last forever. It’s already been resurrected with two new seat stays after a major fight with a car. They all weigh 8kg or less.
They’re all good for sub-5 hour 100 mile sportives. The steel one has more heft for the hills, but it’s still only 8kg.
the things, imho, that make the biggest differences are wheels, riding position and brakes. Wheels don’t have to be the lightest - lightness helps if you spend a lot of time on hills though. A pair of wheels with Chris king hubs will cost around £1200 now I think. I personally prefer rim brakes to discs, but I know I’m unusual in that, but that’s comparing 105 disc with dura-ace rim. If you’re trying to crack on, an upright posture will annoy you, but will be fine if you’re just getting some miles in.
have a look and see what you can find. You can get a lot for your money if you stay away from fancier materials. I ride on alloy rims most of the time. A cannondale caad whatever will do you well, for example. Finally, have a look at the hills around you as and decide if a wise man would choose a compact headset. Probably wise if you’re not after all-out speed