You can have any number of Job cards in a JCL. The maximum limit is 255. Each job is separately pooled in job spool area, after running a JCL with multiple job cards. A job is a collection of related job steps. A job is identified by a JOB statement.
Differences of INCLUDE and JCLLIB:
// INCLUDE -include Identifies a member of a partitioned data set
(PDS) or partitioned data set extended (PDSE) that contains JCL statements to include in the job stream.
// JCLLIB JCL -library Identifies the libraries that the system will
search for: INCLUDE groups, Procedures named in EXEC statements.
How many characters you need for delimiter:
You need only 2 characters for delimiter. Read more about DD * or DD Data HERE.