Hi there,
There’s a ton of post slider/ post grid options out there, and it like something that works well with GeneratePress and doesn’t needlessly slow the site down.
Unfortunately I’m not sure which one will match your need – the best way to figure out is to try a few plugins and see which one works for you the best.
GP will work with any plugins that well coded and built to work with WordPress themes.
We can’t comment whether it will slow the site down or not either. You can determine this by running some speed tests before and after using the plugin.