Grammatical rules regarding colons

I always use two spaces after a sentence ending with a period, and I have a couple of questions about how using a colon will affect that.

Let us assume that a complete sentence follows a colon: This is a complete sentence.

Should there be two spaces after the colon? Also, should the "t" in "this" be capitalized?

I run into another problem when a list follows a colon: numbers 1, 2, 3, 4, 5.

In this case, since "numbers 1, 2, 3, 4, 5." is not a complete sentence, should there be only one space after the colon? Also, for the same reason, should the "n" in "numbers" be a lowercase n?

Thanks.