Saving Configuration for all settings

[Selur]

What is strange that CRF setting at either 18, 15, or either 12 value makes encoded the same bitrate ~10Mbps file.

Might be VHS just does not have enough details/resolution that would require bigger than 10Mbps bitrate to encode at specified Rate Factor, t I am in doubt.
Is this right?

Depending on your other settings especially VBV it might be that x264 is saturated for that source.
To be sure try what happens if you use lossless encoding('constant quantizer (1-pass)' + Quantizer strength 0 + lossless) to see the maximal bit rate x264 would use to archive a lossless copy of the content you feed it with.

So I switched to Specific File Size/Bitrate (2 –pass), setting 22500kbps for Blu Ray compliancy.

might be a waste of space, might be okay,... you need to look at the output.

But which one is recommended: CRF, Average Bitrate (1 pass), Specific File Size/Bitrate (2 –pass)?

I would say:
crf: is recommended when you do care about an average detail retention and do not care about file size
2pass.: is recommend if you aim for a specific file size
abr: I do not see any scenario there I would recommend abr encoding of offline files (might be okay when live streaming, but otherwise I see no use for it aside from testing stuff out)

Cu Selur