Can you add stat boosts to accessories like wings, hats, etc, and if so what items are used? Thank you

Yes, you can add bonus stats to each ''dogi'' as you described.
However it requires you to use clothing property balls, they can only be gained by events and cash shop.

Here a link to where you can buy them cheapest, and how they look like.
http://dbo.wasabii.com.tw/DB_WebShop/page.aspx?PID=303

300 cash points for 30 clothing balls, avarage of 10 Cash points per ball.
(1000 cash points is 32 dollar.)

Why would you need 30 of them tho?

Often you dont get the dogi item effect your looking for in one try.
Since you have

Dogi, hat, glasses, halo and wings thats five pieces, using 30 clothing balls is nothing weird.
Also note, when you use a dogi ball you have 80% on a ''succes''.
If it fails your dogi will be lost and you gain a small chest containing 1 wagu coin, a yellow clothing ball, or a red clothing ball. (red clothing ball has 100% succes i think)

Best allround dogi effects are
Dogi - 10 con / 7% LP recovery
Hat - 10 Soul / 9% physical critital damage / 19 physical attack
Glasses - 10 Focus / 7% cooldown reduction
Halo - 10 DEX / 4 physical or energy critical rate / hitrate
wings - 9% energy critical damage / 19 energy damage / 7% EP recovery


Keep in mind, even if level cap raises, your dogi item effects will always be with your character.
You might replace your items, but always keep your dogi's.

This doesn't work with Dojo Dogi's..?

no, sorry

It does work with the ninja dogi you can buy in West city from medusa points.

do you know when the next event for these clothing balls is going to happen or is it random?

Keep a eye on wasabi events, the last one was previous week and also this week i think.
If you login every day for the whole week, you get 2 dogi balls after the maintaince.

last week only , now it's this:

14 have on-line, threw 5/10-5/23

EV fortune cookies x10
EV LP restore drug pitcher (100 000) the
EV oblivion Appendix X 3 (I wonder what this could be)
EV dance empty Tips primary reel [1st] X 5

also when logging in for these kind of events keep in mind that you need to log in every day in the local time of the game , at the last event I logged in the last day in my timezone , but in the next day in their timezone :(