I think moving from the S90 to a Sony A6XXX series will not be easy for certain shots as the flash sync is only 1/160 so for macro this is a serious limitation
For the wide angle balanced light shots this sensor has some serious qualities and there is very little difference between 6000 6100 6200 6300 6400 6500 looking at real life shots
In terms of lenses starting with the WWL-1 is a good option but you can also get a Tokina fisheye with metabones adapter that will be way more compact than the WWL-1 but clearly is a fixed port choice
For the wide angle balanced light shots this sensor has some serious qualities and there is very little difference between 6000 6100 6200 6300 6400 6500 looking at real life shots
In terms of lenses starting with the WWL-1 is a good option but you can also get a Tokina fisheye with metabones adapter that will be way more compact than the WWL-1 but clearly is a fixed port choice