The plugin does not require any special server functionality. It require a WordPress instance with MultiSite environment activated. It can run either with Subdomain active or Subdirectory structure. Or it can be used with different domains (on any of above structure), see more details upon Set-up different domains for shops
WooCommerce plugin should be deployed and active on at least 1 site. There is no requirement upon WooCommerce activation on all blogs, this can run only for some of the sites.
The server requirements are minimum, the code is compact and well organized to ensure a very fast processing. It will not use more resources than a small to medium plugin. Actually it takes under 5% of WooCommerce code time execution. As long as your server run WordPress without problems, this code will run perfectly fine.
There is a minimum WordPress version required as 4.4 which is already available to most of existing sites. It can work with lower versions however the plugin has not been tested for compatibility issues and is not maintained for such revisions.
No modification on files are required, as long they follow the WordPress Codex and WooCommerce development practices. All features and functionality are achieved through filters and actions to ensure a maximum comparability with other codes.