mysql extended server status variables

[blucados]

Here are 3 questions about extended-status
and server parameters.

I have a server with 1G of Ram Dual Cpu running
mysql 3.23.41.
1/ to know if table_cache need to be increased,
what is the maximum rate of opened_table that
must be seen. I read somewhere that 1 or 2
per sec was acceptable.

I have a server that most of the time is in
the [0,2] opened table per sec but can go up
to 100 / sec at peak hour.

Current table cache is 64 planning to
increase to 512.

Is there a way to find the optimal
table_cache value ?
2/ In the extended status what represents
exactly open_files and open_tables. They seem
to be cummulative values but doing diffs at regular
5 min intervals shows that they can grow an decrease.
3/ Is there a way to find an optimal value for
the number of needed file descriptors based on
maximum number of connections, table_cache, number of tables
in database etc...

Any referrence to server tuning based on extended-status will
be helpfull.

Thanks