@WulfyK: Thanks for all this terrific feedback, and please do keep it coming!
Is seeing other people partially undressed or even fully naked considered sinful/disturbing?
In most contexts (i.e. where the observer hasn’t made an obviously voyeuristic effort), it’s considered shameful for the partly naked person; it suggests that they’re immodest and prone to Xaotic behavior. However, like most shame codes, one of its (mostly unconscious) purposes is to justify the degradation of the lower classes; there’s an unspoken expectation that the helots won’t be able to keep it. So nobles seeing helots working half-clad are more likely to feel smug and mildly titillated than disturbed: “Of course they aren’t properly modest, the dirty little animals.”
Do the helots themselves share the upper classes’ attitudes towards modesty?
As the game suggests when you’re defining your level of physical intimacy with Breden, helots don’t entirely share the upper castes’ values. Few are entirely free of those attitudes… but they adapt them to the reality of a life of hard labor (as of course lower working-class people did in the Victorian era you mention) and don’t judge each other for e.g. stripping down when it’s clearly a necessity for work. Only a very neurotic helot would feel the shame of exposed skin with an intensity that corresponds to the contempt the aristos feel for them.
If the MC is helot but stops singing, the noble version of the massacre is presented.
That’s not actually the “noble version” – that’s the “Gellard is more focused on Carles than on you” version. He normally assumes you’re a yeoman child, because what helot would be found inside a wineroom? It takes a second look for him to realize otherwise. That happens if you sing.
And the version where you inadvertently save Carles stops at what I think is the important moment–though you’re right that that leaves out the blurb about Gellard. But the story’s not really about him.
Do gold drachems also exist or is it just a mistake?
Total mistake. Will fix at next update!
If the MC is a helot and can read, it’s said that s/he was taught by an unnamed friendly deacon. Wouldn’t it be better to make Ecclesiast Olynna the teacher?
Oh, absolutely–great suggestion, thanks!
What happened to the third Laconnian pretender after the defeat? Was he killed in battle or captured and executed?
I don’t think that’s known to the protagonist at this point in the story. 
When choosing the weaknesses, how about a choice “Being unlucky”?
I think I’ll stick with a zero stat as the weakness, for simplicity.
If the MC is a female noble and tells Breden that she suspects him/her, Breden calls her a dandy, though the proper female form is dandyzette.
And you’ve taught me a new word! I’m comfortable using dandy for either sex, though, given the obscurity of the declension.
Also, there should be a question if the MC is honest about the trust or suspicion after s/he tells it Breden.
There is – the question just comes several times in the next chapter, rather than the end of Ch 1. Your explicit response to Breden is really about defining your relationship with her/him, more than your actual level of trust.
It is said that the MC has around three hundred followers when leaving Rim Square, but the actual stat is significantly lower.
I just noticed that inconsistency yesterday myself. I’m rechecking my notes, but there should be 292 helots in the Rim Square estates, counting kids down to infancy. 40% are below the age of 14. I’ll make sure the numbers add up in the next update.
How about making the number of followers slightly dependent on the CHA stat?
It is already, though not in the sense I think you’re suggesting. Because of the circumstances in which your revolt begins, no helot is going to stay behind, however charmless you are; and similarly, the non-helots are going to be too scared/appalled to join you (a 2 CHA can do a lot, but has limits).
How many people (helots, nobles, yeomen/merchants and alastors) do live there anyway?
The helots significantly outnumber everyone else. I’ll give a better answer when I’ve double checked my population numbers.
And @idnlun, I picture the clothes similarly.