It looks like the MSX font is very closely based on the original IBM PC font (these days known as CP437), so for the characters that are ambiguous in 8x8 I recommend checking out the 8x14 versions from the PC.

> I wasn't sure whether some letters are upper or lower case, like pi (π), or theta (θ)

Wikipedia says "227 (E3hex) is the Greek lowercase pi (U+03C0, π), but early fonts such as Terminal use a variant of pi that is ambiguous in case, and therefore can be used for the Greek capital pi (U+03A0, Π) or the n-ary product sign (U+220F, ∏)."

> I'm not sure either what's the character between INFINITY (∞) and ELEMENT OF (∈). I checked an old MSX Technical Data Book and it seems to be lowercase phi (φ), but it certainly doesn't look like it.

Wikipedia says: "237 (EDhex) is supposed to be used as Greek lowercase phi, but is mainly used as the empty set sign (U+2205, ∅) and was also used as the Greek phi symbol in italics (U+03D5, ϕ) to name angles, diameter sign (U+2300, ⌀), and as a surrogate for the Latin lowercase O with stroke (U+00F8, ø)."

The joys of low-res, approximate typefaces - glyphs so weird and obscure you can use them for just about anything.