It looks like your mod does nearly the same (but in a different way?) like LTN does. So I wonder if these 2 mods can coexist in same save?

They can, though there isn't much reason to do so other than trying them both out to find out which you prefer, or transitioning from one to the other. You won't be able to have stations that can be serviced by both mods at the same time, so you will end up with separate sets of stations for each mod.

Note that I haven't specifically tested compatibility with LTN, so it is possible there might be issues, but I don't see why there would be. Both mods use their own station entities and methods for controlling trains, so they shouldn't conflict.

Thank you for the long explanation. I now understand it. So LTN is more complex and flexible than SSPP?

I try now both alongside each other, LTN is already researched but game is played only until crude oil processing.

They have different feature sets. There are several things that SSPP can do that LTN simply can not do, most of them being related to the handling of byproducts. SSPP can do things with a single station and no combinator logic that in LTN or Cybersyn would require combinator logic, a global circuit network (or radars), and multiple stations. There are also some things that SSPP can't do that the other mods can, though most of those things are things I chose not to support as they would make some of the other stuff SSPP can do much more difficult.

Just because SSPP is much more GUI focused than the other mods doesn't mean it is less powerful. I chose not to take the "all of the settings are signals" approach because I wanted stations to be more flexible, without it being overwhelming (I can put tooltips everywhere in the GUIs, whereas setting all the different options SSPP has by signals would be much more confusing).

I'm (slowly) working on a tutorial/demo video that will go into more detail on the ways that SSPP differs from other mods, though it likely won't be done for at least a couple weeks.