Your tempo should always reflect the note value on the bottom of your time signature. For instance, if your song is in 4/4 or 3/4, list your tempo to the quarter. If your song is in 6/8, list your tempo to the 8th note.
We like the stems to be nice and loud, but not to the point of clipping. Your stems shouldn't make the master peak over 0 db (with click and cues muted). Make sure you're bouncing with "normalize" turned off. After you bounce your stems, pull them into your DAW to double check the levels are what you intended before submitting again.
You can apply to be a producer by clicking the Upload button and choosing "Tracks to Sell". If you're approved, you can begin selling your tracks on Loop.