how can i keep my multisite online?

how can i keep my multisite online?
im starting a web hosting company
https://premium.wpmudev.org/blog/web-hosting-design-business-wordpress-multisite/
when i add a lot of plugins and themes it slows down a lot(my network admin and main site admin panels slows when i perform actions takes a long time to complete like loading and refresh takes 5 min or longer for example but loads fast with no plugins and themes) and starts to go online and off line all the time how can i fix this:

Hi bgvsbb.com ,

Jetpack Monitor is on the job, keeping tabs on http://bgvsbb.com . During our last check on Thursday, February 5, 6:21 pm, we noticed that your site was down.

If you’re concerned about your site’s status, you might want to get in touch with your hosting provider. We’ll continue keeping track, and will let you know when your site is up and running again and the total downtime.

Cheers,
The Jetpack Team

Hi bgvsbb.com ,

Good news — your site http://bgvsbb.com is back up!

Your total downtime was 8 mins, but your site was up again as of Thursday, February 5, 6:50 pm.

If it goes down again at some point (we hope it doesn’t!), we’ll be in touch.

Cheers,
The Jetpack Team