The HPL3 tool set is kinda similar to the HPL2 engine editor wise but it is a completely different ball game when it comes to everything else. Since SOMA relies on scripts to run everything that means that there are way more options to tick for it to be different than everyone else's.
You will REALLY like the editors. It is basically the same as the HPL2 editors except there is more customization to it. The shadows are better the asset are better looking it's just great fun to use. You can get gorgeous screens from just the god damn LEVEL EDITOR most of the time. Even if the mod sucks the art will still be a marvel to look at most of the time (compared to Amnesia). Also, there is now moving decals that can have speculars and bump maps which was always a lacking element in HPL2. At least try the Level Editor.
You will most likely get a bit bogged down with the scripting. There is now so much to do just to have the maps work now. You not only have the Start, Enter and Leave functions but there are also places where you put the terminal code, the update code, the general functions code it's quite frankly a mess, definitely a few steps backwards when it comes to accessibility. And don't get me started on making your own enemy!
Overall, you seem to be the type of modder who likes to go above and beyond the call of duty when it comes to scripting so
I think you'll have your first SOMA mod in good hands. I can't wait for your last Amnesia mod too.