> the watts measure the maximum wattage it can handle, so if I need a 27K metal film resistor, 1/2 watt, 1%, would it be ok if I got one at 1 watt? I think that would make the tolerance 5%, so that might not be ok. Another one I need from them is a carbon film resistor, which already has a 5% tolerance. So I would assume a higher wattage would be ok since the tolerance is already that big.
Tolerance and Watts are VERY different things.
Yes, there are trends. Precision resistors are usually "small-medium" power. High-power resistors are usually needed in places where no great precision is required. However you can find, or order, high power resistors of very good precision. It used to be that you could not get high-precision in very-very small Watts: if a precision resistor runs hot, it isn't so precision; anyway americans can't do tiny and exact at the same time.
Generally, the watts shown on the plan is a minimum. A higher-Watt resistor will work, within reason (a 100 Watt resistor in a wide bandwidth amp may add too much stray parasitics). Actually, most designers don't bother to calculate the watts of every resistor. And if you are working with 30V (or +/-15V) power, then a 27K resistor probably can't be dissipating any more than 30V*30V/27K= 0.030 Watts. A 1/2W, 1/4W, 1/8W, or even a 1/16th watt resistor would be plenty. But it is insanely tedious to calculate all the watts, and buy different parts: most designers pick the cheapest size and use it everywhere they don't need something bigger.
When I was a boy, 1/2W was cheapest, 1W and 2W cost more, and 1/4W didn't exist. I see now that 1/4W is often cheaper. If I specified a 1/16W resistor, because it only needs 1/16 Watts, I probably could not find one and might have to pay a lot of money.
Tolerance is often over-rated. In most places in audio, 10% tolerance will work great. 5% is now the low-price standard, and you sure can do good things with just 1/4W 5% resistors. There are a few places where a pair of resistors can both be off by 5%, but should not be off more than 1% from each other. In production you specify tight tolerance so any two resistors will work. In DIY it is often expedient to get a strip of 5% resistors and measure-out matched pairs.
Metal film and carbon film.... I can't believe it will make a BIG difference either way. Metal is good in many ways, but very expensive. And some very fine gear was made with carbon dust (composition), which is much less perfect than modern carbon-film. There is apparently enough "looseness" in the old carbon-composition that it is prized by certain guitar-amp builders, it gives a special tone. But modern dirt-cheap carbon-film is really better than any non-exotic resistors available 30 years ago.
Metal film will hold together at higher temperatures than carbon-film, which may be why you are finding it in the larger wattages.
I think an SSL could be built with nothing but 1/4W carbon-film resistors, which are cheap even in 2% tolerance.