How many RPS can a single Yo!Kart instance handle on the recommended hardware? What is recommended hardware?
For Big Marketplaces, a horizontally scalable application server cluster is a mandate; so, any configuration with or above 4GB RAM should be good enough to launch.
RPS on a single instance depends on several factors e.g. the number of products in the system, the number of attributes set for each product and other configurations set by admin/setup/customizations. Yo!Kart in itself is a highly configurable system, estimating resource requirements of a request is almost impractical but can be analyzed by time based on the data i.e. server logs and website traffic analysis.
From our experiences, one single T2.medium EC2 instance on AWS (with mySQL is installed on the same instance), Yo!Kart can easily handle 200-300 users per day with around 20-30K products in the system.
To add further, You may need further optimisations in SQL queries after your setup and scaling to improve the performance with your customizations and/or setup.