The set of plugins that you pick and use on your child sites is key to how well your site will perform. Taking the time to review the plugins that you use for specific features and functions is key to making sure your site does not run into performance issues or cause performance issues.
Always pick well-known plugins for key site features be they free or paid plugins. Check the reviews if the plugin is on WordPress.org as well as the type of issues that show in the support threads.
One way to find out which of the active plugins on your site are causing performance issues is Query Monitor which will show slow queries, as well as database, queries happening on your site. The Query Monitor plugin well for a shallow dive into database issues happening on your site.
One of the best methods to deep dive to find which plugins are causing performance issues, the most common database queries, slowest queries on the site as well as the slowest external calls is New Relic APM. A number of hosts include integration with New Relic so all you need to do in a lot of cases is to add the New Relic APM account key and install the WordPress plugin on your site.
New Relic APM does not cause any performance issue when used on your site a good example of looking is the external calls to services from the site would be for a plugin that calls an API and when looking in the data in your dashboard in New Relic to find which of those external calls are the slowest since they will affect the performance of your site.
Masking plugin stack issues with full-page caching plugins does not fix the root issues that are happening on your site all it does is fix the issue from showing on the front-end of the site. Also the same goes for throwing more resources on the site’s server you are only going to run into the same issues. If a plugin is stacking slow queries in MySQL on your server then those will still happen it will mean that you run into SWAP and CPU issues slower but the root issues will still be there.
All it takes is one or two plugins that kill your site’s performance and show up on the front-end of the site or in the back-end of your site in wp-admin. I have covered which plugins do cause issues and which of the common ones to look for WordPress and WooCommerce