I don't know much about the conventions of one nation/culture vs another, but I do know a great deal about typography.

Most of our rules and practices evolved back in the dark ages, when the available technologies for rendering language in visible form were pretty much limited to handwriting, typewriting, and typesetting. Only in type-for-print did one have options to italicize and/or make boldface, and to change size or typeface.

Now that everyone with a computer/word-processor can duplicate (or at least approximate) full-fledged typography, many of these traditions are being forgotten, which has created a bit of confusion in certain situations. Examples:

Copy to be set in italics was/is rendered in typewritten (or even handwritten) form by underlining. In other words, underscore = italics, which in turn means that no word or phrase should be both underscored and italicized; according to long-established tradition, that would be redundant.

Typists, for generations, have been trained to insert two wordspaces after each sentence-ending period. Because typewriters have always produced monospaced output, there is some logic to this convention, since it helps make the end of each sentence more clearly visible. When rendering text into typeset form for printing, that double-word-space is a definite no-no. When typographic technology first began using the QWERTY keyboard for electronic input in the 1970s, and experienced typists were being hired and trained to set type, this was a VERY difficult habit to break. (Also, when later technology allowed word-processing files to be captured electronically and converted for use in typesetting, algorithms were normally included to search out [period-space-space] and replace each instance with [period-space].

Back to the original basic questions:

I lean towards the practice of capitalizing all "important" words in titles (which, I realize, leaves a bit of wiggle-room for interpretation regarding which words to capitalize). And of course, the first word is always one of the "important" words.

No punctuation at the end of a title except, when appropriate, a question mark.

In lyrics rendered line-by-line, I observe the same practices appropriate for non-musical poetry:
~ Capitalize first word of each line (and nothing else except proper nouns);
~ Punctuation at the end of a line ONLY in cases where a given mark (comma, etc.) would be used in prose or any other context.

One interesting practice occasionally used when typesetting poems/lyrics is to indent alternate lines. I do not know of any "rules" governing this practice ~ can anyone enlighten me?

When "typesetting" (word-processing) song-lyric "cheat-sheets" for myself, I'll do whatever it takes to fill a single letter-size page using the largest possible point size. For song lyrics with short lines, rendering line-for-line will result in too many short lines, necessitating use of a small typesize and resulting in a page with a narrow column of type down the left-hand side with a large expanse of blank white space to the right. It is usually much more practical to combine two or more lines on a single typeset line, separated by virgules:

short first line / short second line
short third line / short fourth line

When the lines are long, and/or when short lines are combined to make single tyeset lines as above, the alternate-line indent method can make it easier to find the correct next line when the eye jumps for the right-hand end of one line to the left-hand-end beginning of the next:

short first line / short second line
    short third line / short fourth line
short fifth line / short sixth line
    short 7th line / short 8th line