_Blender

Blender is a ridiculously powerful topographical modeling program, capable of complex physics simulations, Photo Realistic Renders , Animation, and Topological CAD modeling.

In short : Quads are better than Triangles for Good Surface Topology but take more memory. If you're designing a game, memory is likely something worth optimizing. Whatever you do, don't use N-Gons.

Settings

Rendering Optimizations - Reduce your settings until you start to notice, render that and save Oodles of time.

Resources

3D Asset Search Engine - Aggregates and Fuzzy searches through the common Sources

Polyhaven - Excellent Free Everything

Fab.com - Not Free But master Quality models primarily geared towards Game Assets

AmbientCG - Free Collection of various items

Poliigon - Incredibly Good Paid Models

Blenderkit - Resource of Free and Paid resources