Crowbar VS CompilePal

To edit the textures, you can use Paint.NET (https://www.getpaint.net/), and for decompiling and compiling, use Crowbar (https://github.com/ZeqMacaw/Crowbar/releases).

If you use the Crowbar tool you can extract files from VPK's.

TF2 and Portal 2 are different branches of Source. the models don't always work well when just dragging and dropping. crowbar can decompile and recompile entire folders of models at once

You will need VTFEdit for the textures, GCFScape for extracting, Crowbar for decompiling the model and Blender Source Tools for importing the model.

Crowbar is the go to compiler helper https://steamcommunity.com/groups/CrowbarTool

it a program/modding, where you can create custom models. but i do recom learn how to use it, heres the official group: https://steamcommunity.com/groups/CrowbarTool

Most models from CS:GO are in Left 4 Dead 2 so I recommend looking for them there first because the conversion is easier; for de/recompiling use Crowbar

Use GCFScape to export the .mdl from the CS:GO VPK (in the "csgo" root directory) and use Crowbar to decompile into .smd. You can then use Blender Source Tools to open the files in Blender, where they can be exported to .obj or .fbx if necessary.

Warmly recommending to pair hammer++ with Slammin' source mapping tools(compilers) and compilepal.

Error boxes means missing props - you need to pack your custom assets into your bsp. I recommend compile pal though other options are available (pakrat/packbsp/vide)

compilepal can be used to pack assets into the bsp.

You can also just use Compilepal for compiling your maps https://github.com/ruarai/CompilePal

Download CompilePal if don't already have it (you may need a pre-release version for CS:GO, since the last "stable build was 3 years ago and stuff might have changed)