The other characters seem fine, but this one seems odd to me:

Is this meant to be the number that is approximately equal to 22/7? (The rest of this email assumes that this is the case. If this is meant to be something related to the pion or another use of that Greek letter, please ignore this email.)

In that case, whether it should be italic or not depends on your mathematical typesetting tradition (for instance, French traditions use upright type for all lowercase Greek, Anglo-Saxon traditions use italics for all lowercase Greek).

Conveniently, ISO has guidance on that, in ISO 80000-2:2019 Quantities and units Part 2: Mathematics, whose Clause 4 says that mathematical constants and functions that do not depend on context are in upright type, and explicitly gives the example of π.

Given that, and given also prior practice in WG 9, it seems to me that it would be best to use U+03C0 π GREEK SMALL LETTER PI as the identifier as the identifier for π.

(And then users who happen to be mathematicians can merrily use 𝜋 for, say, a permutation, without shadowing π 🙃.)

Best regards,

Robin Leroy