The "o" sound in "pauvre" should be pronounced like "coast", not "cost" (except in Marseilles, maybe)
I don't get why we can't just use est instead of soit...
Because of bien que... It is a conjunction which is using with subjunctive and which is about subjectivity
Think of the translation this way, "Though he be poor, he is happy"
I'd imagine that bien que is an expression that triggers the subjunctive, like how "though" in archaic English triggers the subjunctive. Shakespere says: "Murder, though it have no tongue, will speak." (not "has no tongue")
And that is the most important thing ;)
Seems like theres no rule for when soit voie aie ends in either t or e