can QB handle a database of 250M records

If your 250K records have less than a dozen fields AND you are not making extensive use of relationships, yes!

One other idea.

CloudBase Services can integrate Quick Base with a SQL database on your server, Amazon or anywhere in between.  The other database can hold millions of records and Quick Base can "call on" the records to show your users any data they need.  Contact us via our website for more information.