I'm all for 1 by X setups, they work very well for a large number of purposes, but I think you're pushing the limits here. I'm not entirely sure that a 10 speed cassette is your best option, especially for a rain bike, cutting back to 8 or 9 speeds would likely give you a much longer chain life and lower maintainance.

A 24 tooth chainring is tiny, I have bikes whose lowest gear would be higher than that high gear; I would suggest upping it to a 34, it would make finding the appropriate crank easier too.

Don't worry too much about chainline, the great thing about a 1*X set up is that you can use different length bottom brackets to get the chainring exactly lined up with the middle of the cassette. There really isn't any cross chaining to speak of. Throwing chains can be an issue, but there are a multitude of solutions. Paul makes a thing that's pretty much a stripped down front derailer, you can strip down a front derailer, or you can use something like Salsas 'Crossing Guards.' They all work.