Back when I was doing lots of German stuff, one of things that worked best for me was to have several company's vergions of Feldgrau. None of them quite matched each other, which allowed showing some difference in uniform parts.
The black uniforms are really best using NATO Black as a base, but you have to go easy on the shading.
The camo is an entire exercise unto itself--there are many threads on the topic, and more than a few youtube tutorials
For belts, you need a semi-gloss black, which can take experimentation with your supplies. For boots, my preferred method was to start with a panzer gray base, then wash in semi-gloss black to give depth. The soles get stippled with a pale gray on the wear surfaces.
Tank crews probably ought have oil spills and grease stains and spots where fuel has soaked in. The hard part is in not over-doing it.
You will want to research specific units and get details like piping color right.
Unlike 30 years ago, we can perfrom extensive image searching on google to help in this.