Depends what sort of transactions and how entered.  I have done this level of GL journals transactions pushed in through a Realisable IMan integration. Sage 300 handles it very well.  It can take a while to process, especially if optional fields are involved.  

There might be a couple of limits you need to watch for, depending on what you are loading and how you are loading it.

I actually ended up with 4TB database after 3 years so the only other issues are standard ones around management of very large data.

How long it will take? I have one case with up to 40K line items of OE shipment and Invoice and day end process it will take up to 5 hours to finish all those processes. is there any way to improve this performance?