If I were to attach a 5tb external drive to each of my miners (about 30 live atm)
Would the fact I only have 8mb upload speed total hinder sia token rewards?
Not really. Hosts are currently not selected based on their bandwidth, so you should get the same number of contracts regardless.
Also what kind of resources does it take from each machine?
Up to ~500Mb ram if you're running just a host. Some CPU but not excessive. Mostly during IBD and startup.
Next version are addressing RAM and CPU usage so this will be brought down soon.
Very rough average return in sia coins per day for charging the going market rates?
You might earn about 50 - 100 Siacoins / GB in the current market. There is limited uploading going on, due to renter limitations (again, being worked on by developers).
You probably will not earn a lot on Sia in today's market. Your disks will most likely not fill up. Earnings might pay your electricity. You will support the network, development and get some experience that might be valuable to you when Sia starts running full steam.
Important about running a host: you receive your earnings only at the end of a storage contract (usually 6 weeks). So, you want to keep your host running at least for that amount of time.
Thanks for your answers. Interesting stuff.