Welcome to our group Alex,

I second Alex B .

The useable parts are now more easely available, and we will point them out for anybody asking about those.

I started robot building in 2001, and had no clue whatsoever. The basement still holds hidden, but useless treasures from those days. Wasted time and money getting those...

it's also a question of what your capabilities are, and the acces to tools. Many a machine were build with just an anglegrinder and handheld drill, in about every weightclass. But having acces to more machines and tools speed up the proces greatly, and enlarge the pool of possibilities.
But take care, 1 resource is finite. Time.
If you spend 4 weeks to mill the gears for an über-gearbox, those are 4 weeks not used for anything else.

Another piece of advice. And again, it's that time issue. Search for teammates.
With more people, you have more time to build, even if nothing else comes with the team. But in most cases, it means also more other resources.