Starting my second try on Krita. Already feels much better than some years ago, it's usable and quite stable now
I stumbled across some annoying little layer problems though.
But maybe it's just some hidden option or shortcut I can't find, so please help if you have more information.

1. Is there any way to delete a hidden layer, or do I always have to make it visible first?

2. When I transform a layer which is in Normal mode, then I always see the final effect while transforming, which is cool. But when the layer is in a different mode like Multiply or Overlay, it always turns back to Normal while transforming, and in most cases I don't see what's below and I don't see what I'm doing. Is there an option to deactivate this? So that it would stay in Multiply mode while transforming? Same with visibility, it always turns to 100% while transforming, which is not good when I want to transform based on something that is below the current layer.

3. Is there a way to select multiple layers at once and do things to them? Like transforming or color correction?

1: for now, no -- you have to make the layer visible/unlocked to delete it. It's a todo for 2.9 to change that, it's not difficult, just takes a little bit of time
2: no, that's not possible, and probably won't be possible. The preview you get is not the actual thing, but a shortcut to make interactive performance possible, and that precludes doing the actual composite mode
3: in current development builds, yes, that's possible, but not all actions work yet. Please report bugs for actions that don't worn and which you need in your workflow.

1. Great, I'll wait

2. That's a pity, it makes it really hard to work if I don't see the layers below, especially if I have a big layer which covers all the image space and I want to adjust its position to something underneath.
In Corel Photopaint it seems they solve the performance problem by pixelating the image while transforming (so it appears low res, but still I see it with the final blending mode and opacity), maybe this could be a solution? Or maybe decreasing the color depth while transforming?
Also there seems to be antialiasing when transforming in Krita, doesn't this eat up much of the performance?

3. Works in 2.9 pre-alpha, cool!