Interesting on the Han Nom. Seems to be another Ming variant, though I haven't installed it yet to try out.
The best font I've tried so far is one I can't afford and only tried while I was on a professional printer's computer for a bit. It's a Hei font and is quite excellent for a digital reader I suppose. I've not come across much research on readability of line/paragraph with different typefaces...just independent character legibility comparisons where the Hei/Yuan were generally more legible as independent characters. I wonder how/if the serif components of Ming fonts actually facilitate reading lines the way they do in Latin text, since the word representations and spacing are a bit different. I've heard mention with regard to Japanese fonts that some serif versions are less preferable when using horizontal alignment.
I went to the bookstore to check for examples of Hei fonts in novels, but found no examples of it as a dominant body text in a novel. I found it was used as
bold text in many books that used a standard Ming face for the body text, but the only books that used predominantly Hei fonts were books on design and art, which are all typeset horizontally. English equivalents all use sans-serif too, including body paragraphs.
I found FangSong to work reasonably well, but fairly weak as a face, and not very clear when looked at closely. Same with the few Kai fonts I've got. Both of those I've seen in novels, albeit quite rarely as dominant text (excepting educational books where FangSong is primary).
As far as TeX arrangements for vertical layouts...I think that's been one of the frustrating things for many typesetters to figure out. Have a gander at
this thread in Chinese, or its
Google Translate page. It's not 100% clear but it may prove to be a handy start.