Licence type?

Licence type?

Can someone give some advice here please?
I am considering purchasing a full licence for a large project and unsure on which licence is right for me and even if Zoho projects is the answer.
A bit about the project:
  • there will be 19 users
  • project duration: 3 years
  • will likely attach approx 5 docs per month ranging up to 10 mb each
  • There could be up to 5-6 project meetings per month
  • Archiving - although I will have a back up of documents, will everything be backed up by Zoho? such as forum posts, chat etc?

The top licence with 30GB - is this 30GB of space for the full duration of the licence or per month? can someone please give more information?

Any advice is appreciated.
Thanks,
Laura