The first thing I do with a wide fit boot is press my thumb into the side of it, just above where the ankle bone sits, because that's where a boot either gives you room or quietly digs in all day. If there's no flex there, it doesn't matter how roomy the label promises the toe box is, you'll feel it by the time you're walking back from wherever you went.
Colour wise, I'd always go for something in brown or black before anything pale, because wide fit boots already have more surface area to show scuffs and watermarks, and a lighter tan or a grey suede shows every bit of autumn pavement grit within a fortnight. A deep brown leather or a matte black hides general life rather well, and both go through fit struggles without drawing attention to the extra width the way a cream or a stone colour does, where the eye reads width faster on a pale shade. If you want something with a bit more personality, a dark green or burgundy works in the same forgiving way, as long as it's not shiny, shiny patent in a wide fit tends to look stiff rather than roomy.
On sizing, the mistake I made for years was buying my normal length in a wide fit and assuming the width was the only thing that had changed. It isn't. Wide fit boots are often cut a touch shorter in the shaft to balance the extra girth around the calf and instep, so a boot that's generous at the foot can still grip uncomfortably at the top of a higher ankle, especially with thick socks or tights underneath. Check the ankle and instep separately from the toe room, because plenty of wide fits solve the front of the foot and completely ignore a high instep, which is usually where people end up with a boot that won't zip past the widest point of the foot even though there's loads of space up top. If you're between sizes, go up rather than relying on the width fitting to compensate, a half size up gives room for thicker socks in winter without the boot gaping at the heel in milder weeks.
These do badly with very skinny, cropped trousers that stop right at the ankle, because the extra width at the top of a wide fit boot next to a narrow trouser leg makes both look slightly wrong, like they've been borrowed from two different outfits. They sit much better with a looser leg, a wide jean or something that skims rather than clings, and they're far better suited to autumn and winter than high summer, when a wide fit boot in warm weather just feels like you're carrying more shoe than the day needs. Buy for the width across the widest part of your foot, not the length, and get the length right separately.