I am considering training a Raticate with the following moves:

Super Fang
Inversion
XXX
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The theme is to use Raticate's high speed to bring the opponent's health down to 1/4 with Super Fang, and when Raticate's almost knocked out, finish the rival Pokémon with a strong inversion. Now, there are still 3 questions:

1.- What object would you equip it with?
2.- Can Inversion be a critical hit? If so, would it pay off to add Focus Energy?
3.- Do you think it's wise to put Rest to it, so it may recover after taking all the damage necessary to use Inversion strongly?