How many plugins or maximum load time

It is clear that there is no maximum of number of plugins for a site to work well. It all depends on the quality and the impact that the plugin has on the site’s load time.

I am using the P3 plugin to measure the load time. What is considered to be an acceptable load time? I have read answers on forums that vary from 0.3 to 0.5 seconds.

All feedback welcome.