A big thanks to ultimatemegax who
translated the HSI BD notebooks that's full of staff interviews
Just from memory some things that stood out to me:
-This was in preproduction a darn long time since talks about it started after True Tears ended (so canaan and angel beats got made in the meantime),in fact Kishida Mel was contacted to offer original chara designs for HSI before he was contacted for Sora no Woto but Sora no Woto ended up airing a year earlier than HSI,also at the time it was named "Bonbori Inn" and involved Geishas.
-In the very first concept the protagonist was a woman just starting her working life but producers asked for a younger protagonist.
-Ohana's hair came up a lot
Kishida wanted it to be long and wavy but the animation staff were having nightmares about animating that hair so they asked for short hair (also believing it suited Ohana's personality better) but Kishida insisted on it at least being wavy,even if if it was short,it still gave the animation staff a hard time at first but they got used to it.
-For reference for the bondage scene in ep 3 they really tied a guy up , i'll quote the animation director from that episode,she said: "The young male workers at PA works examined the ins and outs of tortoise shell bondage.It was like they were playing around.The women got exited as they watched the guys.I was working on something else at the time so I didn't get a chance to see them."What?You were doing something that fun and you didn't even try to tell me about it?" (laughs)"
-The original plan was for the 2nd OP to have a fall theme (after the first OP had a spring theme) so they asked nano.ripe for a downbeat song but the song nano.ripe delivered wasn't downbeat enough so they switched to a summer theme for the 2nd OP and decided to have the 2nd ED have a fall theme.