Cool. I like this. The combination of effects is obviously powerful - getting you Legends and making your Legends better - but Wizards do that sometimes.

The only red flag here is the symbol. Enchantments don't tap. You could make this just cost mana - 5 mana is enough that it'll be hard to do that multiple times in a turn anyway. If you really wantto restrict it to once per turn, you could make it something like

> At the beginning of your upkeep / beginning of your end step, you may pay [cost]. If you do, search your library for a legendary creature card, reveal it, put it into your hand, then shuffle your library.