This is very subjective but I’ll give my two cents on this. In my case CFD is more where you need to post-process on ParaView (offline) as for my simple needs FEA can be post-processed online through SimScale’s native post-processor, negating any need to download data. As for when you do need to download data, this is slightly more grey for FEA.
For CFD however, I can give you a decent gauge and which areas of the simulation will give lots of data. For about a 1 million node simulation for 4-5 saved time steps you would expect the total download size to be about 1-2 GBs. This should give you a good gauge on how much data you need. Of course, this changes drastically depending on what you do. For mesh size, obviously the larger the number of nodes, the more data you need to download for the same given number of saved states. For example, a 10 million node simulation for 3 time step saves is around 2-3 GBs. Similarly, this also changes when you save a lot of time steps. For the same 10 million node simulation saving more than 10 time steps will effectively triple the file size and you’ll end up with around 8-9 GBs easily. This is still relatively subjective so your downloads may vary, otherwise its a generally good ballpark.
I would suggest you borrow an unlimited, uncapped internet from a friend, a library or even your school. You don’t want to burst your data caps as I believe doing so would be very costly.
Hope this sheds some light!