You asked
Is the sony a6100 good for beginners?
Yes, I think the Sony a6100 is a good first camera. It's a mirrorless body with an APS-C sensor, which is what I'd suggest to most beginners. It takes the autofocus of the a6400 in a simpler, cheaper body, and mirrorless cameras show you the exposure before you take the shot.
The one thing to plan for is stabilisation. The body has none, so get a lens with OSS for slow shutter speeds. The Sony E 18-55mm f/3.5-5.6 OSS is a sensible everyday kit lens. If you want more reach, the Sony E 18-135mm f/3.5-5.6 OSS covers a lot in one lens.
For more on choosing a first camera, see Your first camera.
Written by Claude from this site's pages.