Don't buy low refines you can get them really easy later on just stack on medium refines through the event and luckyboard is really worth the coupons since you'll get lots of other good rewards

new f2p should use lucky board for med threads. Its the most * for buck

So just burn most of my coupons on lucky board then. What should I get with the points? More med refines?

Yes spend them all on medium refines and max out your gear to the highest level you can get them maybe 6-8 refines if you skip out on this refine event and go for the next one which is a better idea since you can save for advanced refines and go all out but just get low refines through the ranked stores :)

I'm a pure f2p, and Lucky board is one of the only events I spend coupons in. There's occasional other events that I might spend a little here and there, but Lucky Board is my main spending.

I just threw 4k coupons on it today! ;P

how many mediums?

I got about 180+ Medium refines, and collected 1 Charms pack (just to check if it gives me spin, and it doesn't. Lol!), and collected 5 Sage Jiraiya fragments (to keep him at 100, so if I pull him, I can immediately 4* him).