1. spend: use up.

2. thy beauty's legacy: your inheritance of beauty.

4. frank: generous. are free: who are generous.

5. niggard: stingy, miserly person.  abuse: misuse.

7. use: have the use of. —There is an implicit contrast with another common meaning of "use": "lay out at interest, invest profitably"; the youth is using up his beauty, rather than investing it by having children.

8. live: (1) gain a livelihood; (2) remain alive (through offspring).

9. traffic: commerce, dealings.

10. deceive: cheat.

14. Which used lives th' executor to be: i.e., which, if used properly, would survive (in the person of your child) to be the administrator of your estate.