question

In answer to your first question: FlexSim does not impose a maximum on the size of your tables, so how much data you can fit in is constrained by other factors (such as how much RAM you have and how much of it Windows allows a process to use) which are unlikely to be constraining for "just" a few million rows of data.

However, whichever way you do it, it is not going to be fast. However, MTEI suffers from the problem that it will read data cell by cell, which is the slowest possible way of doing it. If the data are only numbers, for example, you are probably better off exporting them from Excel to CSV and then writing a loop to import them yourself.

In any case, make sure that in the Quick Properties window of the Global Table, you check the Use Bundle checkbox. Even if it does not help in the import, it will make accessing the data in the table much faster afterwards, which is already a big help assuming that you will import once, then run often.

If you really want to use such quantities of data efficiently, you are probably better off looking at other solutions, such as putting them in a database. FlexSim has some commands (starting with db...) that allow you to talk to any database using an ODBC connection; I suspect it will beat the Excel import but the real power of that is that you can filter on the database side and not pull all millions of records over to the model but maybe just the ones that you need.