Use the lightmap density viewmode to make sure you have enough to get good quality. If you have a small level you don’t really need to worry about memory or disk space. ‘stat streaming’ can show lightmap memory usage.
Best quality with lightmass is usually achieved with
- High enough lightmap resolution
- IndirectLightingQuality 2 or higher (significantly longer builds, less splotchiness)
- IndirectLightingSmoothness .7 (reduce smoothing to get back contact shadows)
- Disable bCompressLightmaps in world settings. Will make your lightmap textures 4x larger but removes encoding and compression artifacts.