You pay all costs and follow all normal timing rules for the card played from exile with a Junk token's ability. For example, if the exiled card is a land card, you may play it only during your main phase while the stack is empty.

Rose's last ability triggers when you sacrifice a Junk for any reason, not just to activate a Junk's activated ability.

Some spells and abilities that create Junk tokens may require targets. If each target chosen is illegal as that spell or ability tries to resolve, it won't resolve and none of its effects happen. You won't create any Junk tokens.

You can't sacrifice a Junk token to pay multiple costs. For example, you can't sacrifice a Junk token to activate its own ability and also to activate the second ability of Junk Jet.

Raid abilities evaluate the entire turn to see if you attacked with a creature. That creature doesn't have to still be on the battlefield. Similarly, the player, planeswalker, or battle it attacked doesn't have to still be in the game or on the battlefield.

Raid abilities care only that you attacked with a creature. It doesn't matter how many creatures you attacked with or which player, planeswalker, or battle those creatures attacked.