Asvolas

I see. 
I'm not sure if this is doable in Affinity. I'm sure someone will chime in if they know.
 
Have you watched this:
 
https://vimeo.com/147727197

If I understand your aim correctly, you can accomplish what you're after using Blend Options, Luminosity Masking, or you could do this (which - I think - more closely approximates the flow you're after):
 
1) Open 2 versions of the picture (exposure bracketed). I've done this with two photos which I'll call "darker" and "lighter"
 

 
2) Copy the darker picture on top of the lighter picture. Now you have 2 layers.
 
3) Duplicate the darker layer and add a Black and White adjustment.
 

 
4) Select the Black and White layer. From the Layer menu, choose "Rasterize to Mask"
 
5) Drag the mask that results from this into the "darker" layer.
 

Hi Asvolas,
Check this thread (first post) for an overview of what's planned for 1.5.

Hi Asvolas,
Welcome toAffinity Forums :)
It should be out in a couple months (maybe sooner if everything goes well).
There's still a few features to implement.

Hey Asvolas,
 
You can align images using stacking, there are a couple of tutorial videos that cover how to do this:
 
Aligning Images and Stacking: Exposure Merging
 
As you are wanting to merge three separate exposures, at the moment you can only average the exposures using stacking; proper HDR merging is however coming in a future beta, so do keep an eye out for it.
 
Alternatively, once you've aligned the images, you can always merge the exposures manually - there's a video for that too, Manual Exposure Merging.
 
Hope that helps!

Hi Asvolas,
Welcome to Affinity Forums :)
You can use an image stack to align them automatically, then move the aligned layers to outside the stack in the Layers panel or ungroup them.

Hi Asvolas,
Welcome to Affinity Forums :)
You can set whatever shortcuts you want in Affinity Designer/Photo going to Preferences, Keyboard Shortcuts section.
You can also press and hold ⌃(ctrl) + ⌥ (option/alt) while dragging the mouse horizontally to set the size of the brush, and vertically to set its hardness.