Relatively simple question. Is it at all looked down on if I make a sell order at an exchange for a long time? For instance say I get some darkcoin and do the math to figure out how much of a return I'd like to get, then file the sell order in advance before it reaches the price I want. I don't know if this is normal, or seen as polluting the order list or something.
There is nothing wrong with it. Just put the order up you want, and wait for it to execute. There are far worse things to do on the internet these days then filling the orderbook. Nobody will care, because most of the time it is outside the visible range (the orderbook pages from Kraken for example).
Some exchanges may have an "expiration date" and automatically cancel orders that are unfilled after a certain period of time (usually several months). So you should check whether your exchange has such a policy.
Other than that, you can leave your order on the book as long as you wish. Nobody is going to object; in principle, they should be happy to have the extra information. It doesn't really cause a problem in terms of "cluttering" the order book, and anyway nobody except the exchange managers know that the order belongs to you.