Timboli: Well if you don't have a great connection, and you want to do other stuff on your PC at the same time, you probably wouldn't want to risk more than one at a time.
Overall time may be the same, but if they all fail you have nothing, so can be quicker to do them one at a time, because at least you are making progress and system resources aren't being hogged for long periods, especially if you reduce speed.
If it failes you can try to resume, and it could pick up where it left off at. If it outrigth fails then the files are gone.
Downloading more than one won't make it any faster, but overlapping downloads would ensure you are always downloading at full speed overall. Maybe when you're 80% done with one file you start the next. Or if you're going to be away a while do more downloads.
Personal experience downloading giant files at 4k/s, you pretty much just resume whatever it is you're normally doing and check daily to see what the state is, fix it if you have to resume the download, and eventually you get it all.
In the meantime... learn bushcraft, learn a few craft skills, read a book, etc... Or whatever floats your boat.