1.) Should I put YA or 'young adult' in front of my genre?
If this is in a query mail, then young adult is good.
2.) When you have the choice of sending an email query or a letter query, should you choose the letter one instead? I heard some agents don't take emailed queries as seriously. Any thoughts?
Agents take ALL queries seriously. Any one of them could be a shiny new bestseller, doesn't matter which form they prefer.
But most important -- FOLLOW THEIR GUIDELINES.
This is their first clue as to how professional you are. If you are unable to follow the most basic directions, it's a strike against you.
ALWAYS include a SASE in snail queries. It's a Professional Thing and shows courtesy. It's only a 44-cent stamp! Go ahead, splash out!
Do not attach a signature confirmation to your snail query. You do
not want the agent to have to leave her desk, baby on hip, slogging through a rain storm to get to the post office to pick up your signature before delivery query, because she wasn't home the first time to sign for it. (An agent complained about this on the Net and the story stuck with me. The writer didn't make a sale, either.)
If you want to know if the agent got the snail query just buy a simple delivery confirmation. It's only about 55 cents.
Otherwise, a SASPostcard she can toss in the out box is cheaper. It can read:
"Dear Your Name, Your query has arrived at the Their Name Agency."