You can't control where you download at google chrome on android (apart from choosing sd or internal memory) and with the aforementioned inability tobuse extensions, you cannot really use a download manager to control it.
And yeah, you cannot use a download manager app for it either on desktop google chrome either it seems (I'd never put this garbage on my pc so I wouldn't know, search results all tell to use extensions).
I don't know how much ram it actually uses because I'd never put it on my PC and never check on my phone, but it has an infamous reputation for being a ram sink.