Max number of sequence objects
What is a Sequence?


  A sequence is a user-defined schema bound object that generates a
  sequence of numeric values according to the specification with which
  the sequence was created.


MSDN on Sequence definition reference.

Ok, it's a schema bound user defined object. What does SQL say about how many User Defined Objects we can have?


  Database objects include objects such as tables, views, stored
  procedures, user-defined functions, triggers, rules, defaults, and
  constraints. The sum of the number of all objects in a database cannot
  exceed 2,147,483,647.


MSDN on maximum UDF reference.

Summary answer: You can have 2,147,483,647 objects in a database. One of those objects referenced would be Sequence Objects which Sequences fall into that category. This is not explicitly stated, but it can be contrived from the wording "... the sum of the number of all objects in a database cannot exceed 2,147,483,647."