I am about to learn 3D modeling and texturing.
my target is to be able to make buildings and props from WW2.
example: bunkers, fences, ammo boxes, lights, …
Which software should I start learning for 3D modeling and which for texturing and of course UE4 for importing my models.
If you can afford it there are 3DS Max and Maya, then Houdini, Foundry MODO and many other expensive software packages.
Cheaper alternatives can be using Blender 2.80 but the free version alone can be slow to work with (it still relies on shortcuts too much and achieving simple things still requires many workarounds with the UI…which means wasting time, slowing work down a lot) although a huge improvement over the previous versions up to 2.79b in which the UI was a real mess. You can find free Maya UI mimic plugin for Blender and then there is the free Bforartists Blender 2.80 fork which features a cleaner better UI. Still you might need buying some plugins/addons on Blendermarket and/or Gumroad to enhance the Blender 2.80 workflow , there are some cheap enough that can match features found on way more expensive software.
Then there is the Rocket3F Basic V1 free software too which has many powerful modelling features but whenever you need to customize its tools then you must buy the Pro V1 version which is not that expensive.
For UV optimization/unwrapping you might want to check RizomUV which is rent-to-own and not that expensive.
For painting there is the still in alpha/beta stage ArmorPaint which is very cheap. Then there is the Adobe Substance Painter (which is still rent-to-own but Adobe might change that soon).