The official recipes of foods featured during the series run can actually be found on the TV-Asahi Website of Kamen Rider Kabuto under "Makanai", which means "meals." You can access the website using the way-back machine.
Most Riders in the series start off with a bulky-looking armor in their Masked Forms. They would use "Cast-Off" to remove the bulky parts, similar to how an insect would shed its skin. This transformation sequence was inspired
by the Inazuman series, another Ishinomori Hero. Like the Riders in Kabuto, the main character
Goro would transform into Sanagiman, an armored brown pupa. When Sanagiman accumulates enough kinetic
energy, his brown pupa explodes, revealing the blue moth-like mutant hero: Inazuman.
Hiyori's illustrations that were featured in the series were actually drawn by Mitsuru Karahashi, who portrayed Kaido in Kamen Rider Faiz. Karahashi actually happens to be an illustrator in addition to being an actor.
Because the main actor Mizushima Hero lived overseas when he was little, he actually didn't know what Kamen Rider was. Producer Shirakura actually chose Hiro Mizushima himself to play Tendou Souji upon meeting him because of how unique his aura was. Usually it's up to the Director and TV-Asahi who makes the decisions but luckily, everyone agreed as well.
The motif of Kamen Rider Gatack is that of a "Kuwagatamushi" or stag beetle as opposed to Kabuto whose motif is that of a rhinoceros beetle.