Hi, and welcome!
You will need different tools for different tasks in character creation.
It all depends on your expectations
Most simple case: For morphing a character and building an advanced custom look,
you will maybe need some more morphs than the build-in ones.
There are some good morph packs at the download section
Though, you can go a long way with only the build-in morphs.
Creating custom morphs: If you get stuck and need a very special morph that only can be done by yourselve,
then you will need DAZ3d and a 3d tool of your choice like Blender.
Remember, VaM and DAZ are using the same "Genesis 2 base figure", so the morphs are somewhat compatible.
You will also need the Morph Merger plugin and the VaM-to-daz morph exporter tool.
For editing and/or creating your own textures, you will need a good painting tool lthat can use "layers" like Photoshop, for instance. Those VaM (or netter DAZ Genesis 2) textures are somewhat simple to understand.
But keep away from those seams if possible! They are horrible to match.
To paint over seams you will need a 3d texturing tool like Substance painter.
For creating clothes completely from scratch, you will need all of those tools and maybe more.
You can create hair styles completely within VaM.
For creating face textures from photos, IMHO the FaceGen tool is very helpful.
Though, forget about "one click and it's ready". You have to edit the results,
and the automatically generated head morphs (which are theoretically compatible to VaM) are not good enough and will need a LOT of post-processing in VaM.
You will need Unity only for creating assets/environments/accessories