Is it possible to have wordpress installed in subfolder (e.g.: example.com/wodpress-installation ) as multisite / folders, and have the folders as example.com/foo or example.com/bar or it must be example.com/wordpressinstallations/foo or example.com/wordpressinstallations/bar
According to this codex entry, it is not possible to install WordPress in a sub-directory and use the Sub-domain install.
However, you should be able to install WordPress in a sub-directory (example.com/foo) and use the other sub-directories for your networked sites (example.com/bar).
Also, check out this entry for more info on installing WordPress in a separate directory and using it to power your root.