Thank for checking out the game!
You could definitely roll with those stat changes at your table, but the way they are in the text here was intentional on my part. Sacrifice is a tricky stat but being a solo, selfish focused character in my mind means you are willing to coss more lines and give up the few things you have (because you aren't attached to many things/people) - it also means you are more likely in key moments to sacrifice yourself, because few folks rely on you, you have nothing more to lose, etc. That's how I see it anyway! Fighting for others lowers your sacrifice because of your attachments - you won't throw your ally to the wolves, you won't sacrifice yourself and leave your family to fend for themselves, etc. Higher sacrifice, in my mind, is about what you have to lose. The less to lose, the higher the sacrifice and the more lines you'll cross. The more to lose, the less likely you are to cross those lines, let others and yourself die, etc.
I like your extra Struggle creation questions too! I was adhering to a 2-page limit here so that's why I didn't dig in further, but those are all good questions if you want to create an even richer Struggle.