Hardware Requirements (Officially Recommended)

My recommendation for storage node on <=100Mbit internet channel is a little bit different because we would like to be a SNO with high-efficiency storage node:

CPU: (1 Core >= 2.8Ghz) or (2 Core >= 2.0Ghz) or (4 Core >= 1.5Ghz)
RAM: 2-4GB
HDD1: (System): USB Flash drive (micoSD card) 16+GB or any small SATA SSD
HDD2: (Storj data): 4+TB with redundancy (RAID1, RAID5, RAID6)
UPS: Any UPS with good battery and interface cable
PSU: Any good PSU that can handle your load + at least 30% power

Storage Node not require ultrafast hardware, you can look around maybe you already have old hardware that you can reuse with zero cost.

Here is a general tested recommendations for hardware selection:

CPU: You can use any CPU that not too ancient and not consume a lot of electricity, starting from Sandy Bridge epoch is a good choice. You can use any Celeron, Pentium, I3, I5, I7, Xeon with enough frequency and cores. I recommend starting at least from 2 cores because all 1 core CPU is ancient. (You can use one core only on VM or VPS/VDS)

You can use ATOM CPU too, starting from N2800 or newer if you already have it. Another good choice is modern motherboards with embedded CPU (Celeron, Pentium).

Also, good choice is single-board computers: Raspberry PI4, Rock PI, Odroid, NannoPi

RAM: 2GB is enough for storage node but for improve RAM performance you can use 2x2GB (1GB is hard to find and no make sense) DIMM module in two-channel mode.

Please do not use ancient DDR2 RAM with an ancient CPU that supports this RAM. You will have bad performance for storage node and not good efficiency.

HDD1 (System): You can use any USB Flash drive or microSD card (is no joke and it will be solid stable), look into MLC USB flash drives (Transcend, Kingston, SanDisk etc.) 16GB or more is good choice. Using USB flash drive we will save SATA port for data drive and add more storage space if needed. Small SSD will be also a good choice if you have enough SATA ports.
HDD2 (Storj data): You can start from any capacity (minimum 500GB), but I can recommend starting from at least from 4TB+ RAID1 or RAID5 storage. If we will start on a single drive and this drive is failed you can lose everything, and deposit too. So, RAID is not an option, it must-have for long term and reliable storage for SNO that would like cooperating with Storj for a long term period.

If you already have old drives for Storj please test it with MHDD or Viktoria before using it on your build.

UPS: UPS is also a must-have feature for good and reliable storjling, you can use any but this UPS should have interface cable and software for graceful shutdown when battery is low. Also, this UPS should have a battery in good condition. Test your UPS with a lamp if you don't know battery condition, it prevents unexpected shutdown and data corruption and loss.
PSU: you can choose any, just to make sure that PSU power is enough for your build +30% or more