Wordpress Multisite for 300+ websites

Hello,

We have a network of 317 website which at the moment use a proprietary CMS and we're looking to move to Wordpress Multisite.

In terms of scalability from your experience running big Multisite installations what sort of hosting we're looking at?

VPS? Dedicated Server? etc etc.

The network currently has 317 websites but each week 3 more added.

Each site gets in average between 100-300 pageviews per month and the main website is getting 120,000 pageviews per month.

Many thanks!