a couple of newbie question - deferrable, varchar vs text, 2 dbs

1) Do I understand it correctly that cross database queries are not
possible? Two dbs on the same server are used in this case.

2) What's the difference between unlimited length varchar and text
columns? I am mostly interested in performance, namely = 'blah' and
like '%blah%' queries over these column types.

3) Will adding "deferrable" to FKs that reference very large tables
speed up insert performance for individual inserts? for multiple
inserts within a single transaction?

Thanks ;)