It's a galactic empire, resources shouldn't be an issue.
I think this is the cardinal error of ROTJ.
The Imperial Fleet there would be a tiny subsection of the ships available to the Empire.
The troops in the Endor land battle would be the normal troops defending such an installation.
The should be building a Death Star for every regional territory at the same time.
Palpatine owns everything and everybody so why the uncharacteristic lack of ambition?