Hi Mark,
since no-one has chimed in I'll have a go at answering the best I can.
I've only done this a couple of times with Orion as I don't do much imaging this time of year and have never done a really deep image of M42.
It's hard to know whether the four sets of data re overkill or not as each situation varies. Even 10 sec exposures can be too long for the core of Orion given how bright it is, although this depends on how much you stretch the image of the core.
Start with two layers and see how it goes & you could always add in intermediate ones if you think you need them.
Aligning the separate images shouldn't be too hard as they should be quite close and the same image-scale. It can be done manually in Photoshop using the move tool, and either 'blinking' between the two layers (by turning off and on visibility of the top layer) or you can use difference blend mode on the top layer (or a bit of both). (You could always try "auto-align layers" under the edit drop down - who knows you might be lucky?)
The hard part is blending it all together so that it looks smooth and seamless. I find the "select and mask" function (from the Select drop down menu) works well allowing you to feather any selection visually, so there's not an abrupt step-change between layers. A fair bit of trial and error is usually required.
Good luck and feel free to post up your efforts.