Hi and welcome!
So, what is the general idea, all in the cloud and Nethsecurity on premisses and VPN to the cloud? Several use Digital Ocean or Contabo
That would make home working/road warrior pretty easy too, also adding new offices
How about storage? Want to go for a S3 compatible storage witha. VPS provider, or use NS VPS onboard storage? I would opt for a seperate S3 compatible object storage.
Per office location or in the cloud? Beware that NethVoice is primarily intended for Nethsesis partners and has limited functionality in the Open Source and unsupported version.
How about the individual components setup such as (web)mail, groupware/calendering, domain (Samba/LDAP) etc?
Just poking around here 
Again, welcome!