For your old PC x Storage Mining, 8 GB of RAM is probably too little for sealing a sector because it’s recommended to have at least a few times the size of a sector in terms of memory. Right now the minimum sector size is 32 GB for mainnet (although all specs may be subject to change) so for testing configurations 64 GB or 128 GB of RAM are used. You could use part of the SSD as swap memory but it may take a very long time to seal data.
You might be able to use your old PC for Retrieval Mining later on though. The Retrieval Market will be further developed after launch and may depend more on locality, bandwidth, caching strategies, etc.
For Windows 10, you can install the Windows Subsystem for Linux to run Lotus with any recommended Linux distro. A Windows developer has tried it and said it works well.
The hardware specs are currently pretty high as @Koru says because the security of the default parameters used in the network are most important for launch. But it’s likely that hardware specs will evolve after launch as the proofs are further optimized and more markets (like for retrieval and repair or outsourcing SNARKs x GPU) to support the protocol and help miners diversify are likely to arise.