How much Memory enough?

How to Tell if Your Site Needs a Shot of more Memory:

If your site is behaving slowly, or pages fail to load, you get random white screens of death or 500 internal server error you may need more memory. Several things consume memory, such as WordPress itself, the plugins installed, the theme you’re using and the site content.
Basically, the more content and features you add to your site, the bigger your memory limit has to be. if you’re only running a small site with basic functions without a Page Builder and Theme Options (for example the native Twenty Sixteen). However, once you use a Premium WordPress theme and you start encountering unexpected issues, it may be time to adjust your memory limit to meet the standards for a modern WordPress installation.

Increase the WP Memory Limit is a standard practice in WordPress and you find instructions also in the official WordPress documentation (Increasing memory allocated to PHP).