Calculate font and baseline sizes

One of the problems with trying to calculate what font sizes may be needed is that if you were to actually measure the height of different fonts of the same point size you would find that they may not actually be the same height. This is because point sizes for many fonts were determined many years ago pre desktop publishing when fonts were cast on metal slugs for use in linotype machines. The size of the typeface was actually determined by the height of the slug needed to support it. So a serif font with delicate features needed a taller slug so that the serifs wouldn't break off. When phototypesetting came in fonts that existed then carried the sizes that they had been assigned so as to avoid any confusion. Many of the older typefaces (Helvetica, Univers, Times Roman, etc.) are still  in use today. As far as I know the height discrepancy has never been changed. So trying to calculate font sizes may still demand a more manual approach.

I don't quite follow the question. Font size, for the most part, has nothing to do with alignment except that (fairly obviously) the line spacing or leading should be equal to, or ideally, slightly larger than the font size. There are subtleties about specifying whether type is vertically aligned by leading, ascent height, x height etc. but those are advanced details; font size and leading, plus any space above or below, are 99% of vertical text alignment.

If you are trying to get precise alignment of the text lines on facing pages and a precisely positioned bottom line, setting and enabling the baseline grid is a useful step, but that can be a workaround/hack that fails to be consistent if you don't make every paragraph style (leading plus spacing) some exact match or multiple of the baseline value. That is, you can set your baseline grid to 14 points (or use 14pt as your base value, without enabling the snap-to-grid feature), but then every paragraph style has to have a total line height of 14, 28 or 42 points if you want things to always align. You can't have a body text height of 14 points and then, say, a heading height of 18 or 24; using that style will throw off the total column height and you won't get page to page or bottom alignment.

It's an art to get it all right, and a mistake to rely too heavily on baseline grid snap to do it all for you.

There have been some good discussions of this recently, with references to more detailed methods and rules and tutorials. Search for "baseline" in this forum.