I wear a US size 7 shoe and I ordered a US size 7 boot. It fits my foot just fine, it's a bit snug with thicker socks. I have perfectly average feet, not too wide, not super narrow, no bunions or corns or other protrusions. If you have wide feet or are planning to wear these with thicker socks, you may want to size up a bit.
The toe box is roomy enough width-wise, and the length is perfect for me, but the upper can be restrictive with thick socks or a thicker, wider foot.

I find these boots to be quite comfortable out of the box. However, they are stiff, and will require wearing to loosen the upper. Eventually it will break and be super comfortable. Expect some chafing above your ankle because again, the leather is quite stiff.

I've been wearing these around England, it's winter here which means wet, wet and cold. These boots are actually quite warm. And they are waterproof to a point. Clearly these aren't Wellies, and if you go stomping around in muddy puddles, some water will make its way in. I wear  them anytime that I would, in better weather, be wearing sneakers. Walking the dog, which is almost always damp and muddy, doing errands, etc. I haven't yet but absolutely would wear them in a couple inches of mud; that's what they're made for.