Only use 1 reflection capture for now, the box or the sphere!
Have only 1 skylight. Play with it’s intensity. If I don’t have a dir light I’ll put the intensity between 3 and 8. (static)
Use a directional light only if you really want your scene to be sunny! (if you use a dir light you can lower the skylight intensity to 1)
Portals can raise build time but also increase the quality of the G.I (just don’t use too many) You could use 3 total maybe.
Try to bake it to see how it looks. Start with preview setting and low lightmass quality setting just to see how bright it is. All the nice shadows are going to appear after your final production build.