That's correct. I've tested it on Linux with some changes (I have no uuencode there, so lines with uuencode replaced by "cat" of text files, and 'Content-Type: application' lines thus removed).
And yes, it should work.
The reason the same boundary used everywhere is that the boundary is defined for the whole mail only once, and separates body from each attachment, and then finalizes the email with "--" appended.