Deep breathing merits past the first are largely pointless. Healing breaths already cure so much, a player's max HP is rarely enough to take a full DB breath.
And using DB for DPS purposes is extremely miniscule. you'd be looking at an extra 440 or so dmg every 5 mins. That's 1.4 extra damage per second. Just the ja delay from using DB would negate that. Even ignoring the chance of letting a melee hit land in breath gear and the resulting haste/stp loss.
I'd recommend 1 merit in DB(just for general utility), and 4 in empathy(5/5 in Angon is a given). More wyvern buffs for increased survivability and DD buffs.
Although, some ppl like to only do 1 empathy so that they can spirit link 5 times before spirit link starts consuming the players HP.(explanation: Each Empathy merit grants 200 exp to the wyvern on spirit link use, triggering his temporary parameter boots. This functions like a level up, in that it fill his HP to full. When the wyverns HP is full, spirit link doesn't consume player HP. The exp bonus caps at 1k exp, or 5 level ups. So at 1/5 empathy, you have 5 spirit links before you start losing HP. Makes keeping the wyvern alive safer.)
But personally, I like to get the wyvern to max strength faster. So 4/5 means only 2 spirit links before the wyvern is at max potential. And you can copy 4 buffs to the wyvern at once.