im dual weild frost and want to try plague leech, whats a good ability to macro it to if any as i like to have as little keybinds as possible
None. Only a bad DK would do that.
What would you macro it too? You just use it and that's it.
Even if it was off the GCD, you wouldn't want to macro it into your attacks for what I hope are obvious reasons.
If you want to save a keybind you could put it on the same button with ALT pressed with a line like
/use [mod] Plague Leech; Scourge Strike
Or you could possibly do something like (for Unholy)
/castsequence reset=59 Outbreak, Plague Leech
but you would need to be careful not to double-tap that key.
Also, unless im greatly mistake, the value of plague leach is in the ability to micromanage diseases to gain an extra death rune for an UH (Basically a HB instead.) Trying to use it any other time except for an optimal time won't help you.
Don't macro it, it's not going to be used in the same situation very often.
Your mouse should have a fair few buttons in this day and age. If you have one of those olden day, non Razer-naga type mice then it should have at least 2 buttons on the thumb pad - would recommend plague leech on one button and HoW on another.