Performance /C++/Documentation

Hello,
    I have 5 problems:

    1- I need precise performances about postgresql. In particuliar I want
       to know if POSTGRES DATABASE can support 50000 or more tables without
       performance problem?. The searches would only use a few of these
       tables ( 10 at best ).

       I suppose the disk storage place available.

    2- when using Libpq is the size of a query limited in a PQexec?

    3- I would like to know how many LARGE FILE is it possible to create
       in the database.

    4- This point is more technical. I want to use the C++ compiler and
       I don't succeed compiling. I have the following error message:

    "../postgresql-6.3/src/include/c.h", line 67: Error: "," expected
     instead of "*".
      BLABLABLA ...

    5- I dont find documentation about the SQL understood by POSTGRESQL.
       Where can I find some. I rather prefer something printable if
       possible.



    Can someone help me. Thanks in advance.

                            Lewest Ph.