<p>What is the maximum size for a MySQL table? Is it 2 million at 50GB? 5 million at 80GB?</p>

<p>At the higher end of the size scale, do I need to think about compressing the data? Or perhaps splitting the table if it grew too big?</p>

About your first question, the effective maximum size for the
database
is usually determined by operating system, specifically the file size MySQL Server will be able to create, not by MySQL Server itself. Those limits play a big role in
table
size limits. And MyISAM works differently from InnoDB. So any tables will be dependent on those limits.
If you use InnoDB you will have more options on manipulating table sizes, resizing the tablespace is an option in this case, so if you plan to resize it, this is the way to go. Give a look at
The table is full
error page.
I am not sure the real record quantity of each table given all necessary information (OS, Table type, Columns, data type and size of each and etc...) And I am not sure if this info is easy to calculate, but I've seen simple table with around 1bi records in a couple cases and MySQL didn't gave up.