Mac Mini server advice yet again

[strm]

Posted in the Networking forum before, but after reading a bit, here might be more suitable.

The ol' Time Capsule has parted from me, and I like to interpret this as an opportunity to step up my game slightly. I looked at ready-made NAS options, but decided against those, so now I'm looking at a Mac Mini server.

What I want to achieve:
a) Time Machine backups for 2-3 Macs
b) Torrenting machine
c) iTunes server for music and film
d) Photos server.

My questions:
1. For torrents (b) I'd like to send Transmission traffic through a VPN and implement a killswitch too. Any (permanent) interference with the other use cases this might cause? What if, in the future, I want to use the server as an internet cloud too - any problems with it there?

2. For iTunes media (c), I'd like to store the library on an external RAID. Thunderbolt is too expensive. Would USB 3.0 (like the WD My Book Duo for example) do the job? How 4K-ready would this be for streaming without any transcoding? And any limitations to transcoding for iOS devices here? Are there any likely scenarios where I would run into bandwidth issues on USB 3.0? It seems either Ethernet or HDD would bottleneck first.
As is probably obvious, I have very little experience with these storage things, so if you have any other remarks, go for it.

3. How do people go about (d) centralising their Photos library? It seems there is no native equivalent of iTunes' Homesharing, is there?

I'd appreciate hearing your thoughts.

 

[ColdCase]

1) Dunno, don't currently use VPN.
2) what kind of RAID? Why do you think you need RAID, why spend the money? USB3 is a bandaid at best for storage, especially RAID. My mini is much happier with Drives installed in a TB enclosure. I use disk utility to RAID0 or mirror. Latency may be an issue for more than a couple users. For something like a TM destination, USB may be an option.
3) There are dozens of ways to skin that cat. You can also share photos via iTunes (just point it to the folder where your photos are located). Will you have concurrent users accessing and editing that photo library? The Photos app, iPhoto, Aperture all can store their libraries (or a public library) on a server volume. I usually store a large collection of public photos in a file folder. Users can view and edit as they wish. A small subset for viewing only is shared via iTunes

 

[strm]

2) Either RAID1, or maybe considering Raid10 if you say I'd see a benefit from the striping for my use case. So doing it for the redundancy mainly.

In what sense is USB3 a bandaid, and what makes the Mini happier about TB?

What determines the latency for more than a couple of users? Whats the search term I need to use to find out more?

3) So neither Photos nor iTunes are able to do the concurrent viewing and/or editing of photos? Is that only achievable with raw folders and files?