It's approaching that time of year where I need think about minimising next years tax bill, so a laser cutter is looking like a reasonable way to at least do some of that.

Previous advise was don't get a red A4 one that runs moshidraw, as they're rubbish (well, that's the polite version of what the now departed John S said). Get a bigger A3 size blue and white one.

Which brings me to the question of what wattage to get?
60W or 80W?

It will most likely be used for some metal engraving (both steel with suitable spray, and anodized alu), engraving wood, and cutting some thin plywood.