Which kind of database is the right choice for a Cloud Based PMS system?


We are a startup company that we want to create a new SaaS Cloud PMS (Property Management System) for small hotels and properties. Also we create a website for booking. The scope is to be able after our solution is well established to provide automatically personal suggestions to our customers.
Since we are on the designing phase we want to create it with latest standards in dbms to be able to be expandable and support big data, analytics etc that it will give us
a competitive advantage.

We have received proposals from different Software Development companies that some of them have proposed different kind of databases.
And my questions are the following:

  1. Are non relational databases suited for our case? And how we can decide with which database we will go?
    What factors should we evaluate while choosing?
  2. What are the extra cost of choosing a nonSQL database? We think that if we choose a more exotic “database” other than the SQL we would have
    problems finding locals to maintain and update our projects.
  3. Are there any companies that act like independent consultants that can consult us on the pros or cons and design the perfect fit for us
    for the database issues and the big data analytics?
    We have found some but most of them seem really big companies that will not deal with a small client like us.
  4. Is a database written on mySQL and have a Hadoop System comparable with a non relational database?

Please let me know since we are “newbies” on that any other concerns that we should have while deciding.

Thank you in advance.