Thanks for your reply, Andrii.
Like HivePress, I believe Kadence is coded with very high-standards, so for someone who knows what they’re doing, I’d expect the integration isn’t too difficult.
Kadence don’t offer a custom page builder like Elementor does that ‘takes over’ the core WordPress editor, instead, they offer another plugin called Kadence Blocks which extends the Gutenberg editor by providing new blocks to design the website with.
I have built several sites with Kadence theme in the past and have never had any issues with speed or weight of the site. Like I said, Kadence is very well coded, and while it provides a great deal of customisation options; it’s not bloated with extra code.