... small sensor pixel area and the reason I got the 35mm lens...
It seems you are confusing "pixel area" with "small sensor". Pixel area is associated with pixel density and does not affect the focal length required to frame your subject. Sensor size does change field of view and framing. FujiFilm X-series cameras and your current Nikon DSLR share the same APS-C sensor size ("small sensor"), so you will still need a 35mm or wider lens to get the framing you're after.
As with other individual camera specs, there's more to cameras than [pixel area]. That said, the X-T10 is likely still a better overall camera than the X-T100. The X-T100, along with the X-A# series, sits at the bottom of FujiFilm's mirrorless camera offerings. They are FauX cameras that use Bayer sensors instead of X-Trans sensors. It is not in FujiFilm's interest to make low-end cameras with Bayer sensors that outperform, even old, higher-end cameras with X-Trans sensors.
The FujiFilm mirrorless cameras I have used include X-E2, X-T20, and X-A5. The X-A5 is horrible in terms of both camera performance and image quality. If the X-T100 is anything like the X-A5, you'd be better off sticking with Nikon than to switch to a FauX camera.
The X-E2 is far superior to the X-A5 in just about every way imaginable except megapixels. The lower megapixel count is also fairly forgiving of older, manual-focus lenses. I'd expect the X-T10 to perform similarly to the X-E2. If so, the X-T10 would be a solid choice despite its age.
The X-T20 performs better overall than the X-E2, but doesn't handle highlights quite as well. The difference is noticeable only in side-by-side comparisons and inconsequential with post processing. If you're considering an X-T20, I'd suggest waiting for the price to drop after the X-T30 is released.
If you plan to get a kit lens, get the XF 18-55/2.8-4. It is very sharp, and about a stop faster than the kit lenses from other manufacturers. Avoid the XC 15-45/3.5-5.6, which is not only a slower lens, but also has a slow, annoying-to-use power zoom.
As with other mirrorless cameras, you can also use old, manual-focus lenses with adapters. This allows you to try different focal lengths at low cost before you purchase more expensive XF lenses.