Nikko: walking from Kegon to Ryuzu waterfalls

I am planning to go to Nikko and would love to see Kegon and Ryuzu waterfalls. Is it a long hike from Kegon Waterfall to Ryuzu Waterfall? if yes, can I ride the bus from Chuzenji onsen to Ryuzu waterfall or do i have to go back to Tobu Station then ride the bus?

Is it a long hike from Kegon Waterfall to Ryuzu Waterfall?

It is roughly 6 kilometers. I walked it, and I don't recommend it. Despite the fact that the trail follows close to the lake shore, you almost never can enjoy any views of either the lake or the surrounding scenery because it is inside a dense forest. And the trail is surprisingly up and down. If you want to walk, then the walk from the Ryuzu Falls towards the Senjogahara Marshland and beyond is much more scenic.

if yes, can I ride the bus from Chuzenji onsen to Ryuzu waterfall

Yes, you can ride a bus from Chuzenjiko Onsen to the Ryuzu Falls. See the basics here:
https://www.japan-guide.com/e/e3805.html#section_orientation