You should really, really get a separate server!
Think about this:
- Security! Keep it simple. Use a single entry point to your network. How many doors are there at your house? There is a reason why a security hole is called a backdoor...
- Separation of concerns: each component does what it's best suited to do.
- Flexibility: You can upgrade the router, and you don't have to reconfigure everything.
- Storage: Think about what are you going to store! Imagine the storage failed. What would that mean? How much work will you need to put to restore the data... if it's even possible. Even the simplest thing you are storing will take effort on your part to restore.
- You should really want to be running RAID 1 which only works on a separate server.
You want a all-in-1 device use a server... any computer will do, even some VPS providers are running on commodity hardware, and handling fail-over in software.
- I prefer x86 for the flexibility of changing components:
- Hardware video decoding for your media server? Add a CPU with better iGPU, or even GPU
- More RAM for your security cameras... plenty of choices even up to 128 GB
- You want your file server with an extra 4 x m.2 running at PCIe 4x4? Skip the GPU and add an expansion card, just good luck getting that data speed over the network
- You want your server to have SFP+ 10GbE... expansion card
- Data security: if one of the storage drives fails, you have a copy on the other one
- HDDs experience data rot. I have a picture from years ago that looks exactly like this RAID1 partially protects against this
- SSDs also experience data rot and have a limited number of writes, though you may never reach it
- Again: Think about what your are storing? What if you lose the data? That picture from when you were younger? That bitcoin key on a HDD thrown in the landfill? Or that website that it took you a while to set up. Some can be restored, but you will still need to put the work into it.
It's no wonder the ATX standard lived so long. The flexibility it offered in 1995 is still valid today. Just think about the effort you are going to be putting into selecting the components for a small factor PC vs... going to any online store and picking any of the components that are compatible