Yes, the B&S book is very good reference Steve – my edition is from 1941.
Also "Running a Miling Machine" by Fred Colvin is quite useful (reprinted by Lindsay Publications). Both are aimed at 'industrial' users but you can always skip over the bits that don't apply to your needs.
However, I'd suggest that as a starter, you read a few articles published in Practical and Popular Mechanics magazines back in the 40's & '50s. They were sponsored by the Atlas Press Company and were really promotional items for their 'benchtop' MF horizonal mill. They are very useful for the basics and I think you would find them useful. As the happy owner of an old MF Horizonal mill, of course it's no coincidence that I have these scanned as PDFs. If you PM me (with your email) – you could probably have them too!
My two pennies about 'mills' – if you only have the space for one mill – then a vertical type makes good sense.
However, if you already have a horizontal mill, then the obvious thing to get (or make) is a vertical quill for it and then you have the best of both worlds. I've got two horizontals, the little MF and a far heavier Victoria H0. Both have vertical heads, in fact my MF has two. They are both 'knee' machines and are pretty rigid in use.
As already mentioned, not too many folk use horizontals these days, so they don't tend to be appreciated that much but they can be very useful tools – you just need a slightly different mind set.
Regards,
IanT
Example below – end milling a part held in an ER32 block