The dair is good from the ledge since it's multiple hitboxes.
I think if you want to work on the wall of pain, the first thing you should practice is fastfalling between each aerial. It makes it look a lot faster, and you get better control over the vertical spacing of your aerials as well (Bair, fasfall retreat, re-jump approach bair, etc). Also practice full hop double bairs. It's not hard to execute, the hard part is getting the spacing correct. Learn the real range of the bair. You can actually even double jump from a SH bair if you do it quickly enough. This can be quite useful, as a lot of non-Jiggly players don't realize this is possible.
One tactic you can try is to end your WOP with a uair to pop them up for a rest or a combo. ANYTIME you are going to land from a WOP, you should either land behind them, or out of grab range.
Lastly, learn how to angle your pounds. A down angled pound is tricky to recognize, and an up angled pound can put you just above a character's grab range. Pound is a great change-up to put into a WOP, in addition to being a really good combo starter, I generally abuse it on people until they prove that they can punish me for it.