The community edition does not have any kind of activation, does not have any kind of restriction. About professional edition has a license activation to prevent cloning, but also as the community are a lifetime. Professional version if more optimized than community, that not means with the community can not hold this amount of data, it means with professional sure goes better.
The repository size is not much relevant, the relevant values are the number of documents, do you have 2 millions of documents, then you have 2 millions of records in the database. If you have in future performance issues they will come usually from a database, what will need some tunning.
Finally when installing professional edition ( as should be done in the community ) should consider disabling some features. Here the question is for what and in what manner the system will be used and then try to optimize what feature really need. Usually, the candidates to disable are the dashboard, keywords, configure search indexing process, probably enable paginations and catalogue repository data in the right manner to optimize the performance. Also, it is important to calculate the hardware dimensions in terms of cores, ram, disk, use SSD for database and repository in another mounting point etc...
The huge repository is not plug & play, forget this kind of ideas. Big scenarios always might be well configured and optimized from the beginning, otherwise, you have a hidden problem what will be appearing in future ( then is more complex to solve ).
