Is it possible to determine mysql pre-allocated memory footprint
Yes, and you absolutely should! Don't set MySQL to have a potential maximum use more than about 80% of available memory.

MySQL has two types of buffers, global and per-connection. Maximum possible memory use is: global buffers + (connection buffers * max connections).

The mysqltuner.pl script will calculate this for you (http://mysqltuner.com/). Here are the values this script uses for calculating:

Global buffers:

key_buffer_size
max_tmp_table_size
innodb_buffer_pool_size
innodb_additional_mem_pool_size
innodb_log_buffer_size
query_cache_size


Per-connection buffers:

read_buffer_size
read_rnd_buffer_size
sort_buffer_size
thread_stack
join_buffer_size


You can find how much memory is currently used from your Operating System.