Meaning, to first download this torrent, and after it finishes, start those 3 other torrents (in parallel), and when they're finished, start this final one. An order of download.
I know that I can set a priority of low/normal/high but it'll download all these torrents in parallel and I've noticed that the lower priority torrents 'eat' some of the bandwidth from the higher priority one. Plus, if I'm to use low/normal/high priority for what I intent to, it's only useful for 3 sets of downloads (this option was never meant for what I'm using it for).
I'm currently running Transmission headless with the assist of Transmission Remote GUI 5.0.1, if it matters.
can I set order of download?
Re: can I set order of download?
Mostly. 
There is a queue order you can control the order of downloads with. For example if you have 10 torrents to download, AND you limit the number of active downloads to 2, then it will process them two at a time in queue order. If you are using the remote-gui the green up and down arrows control the queue numbering. You can change the displayed columns to include the queue sequence number.
If your limit on active downloads is high then it will just process them all. Also, queue order is not preserved if you stop the transmission and restart it.
There is a queue order you can control the order of downloads with. For example if you have 10 torrents to download, AND you limit the number of active downloads to 2, then it will process them two at a time in queue order. If you are using the remote-gui the green up and down arrows control the queue numbering. You can change the displayed columns to include the queue sequence number.
If your limit on active downloads is high then it will just process them all. Also, queue order is not preserved if you stop the transmission and restart it.
Re: can I set order of download?
Thank you! I'll try it and tell you if it worked.