+1 for whole house insulation.
Regarding solid core doors, I selected an option of solid core door for my master bathroom from my builder (IP) but my normal interior doors are standard hollow core doors. So I have direct comparison for both type of doors. To be honest, I hardly feel any noise reduction effect from solid core doors. There is not much difference.
I don't know it's same for most of solid core doors but at least my one doesn't show much difference. And also it doesn't have any expensive feel at all. Design and colors are exactly same but if you tap on the door surface, solid core door has a little heavier, more tight sound. On the other hand, on hollow core doors, you can feel that inside is mostly empty.
If your main purpose of selecting option is noise reduction I don't recommend it since your builder is same as mine, which means there are high chances of getting same brand's solid core doors.
A few month ago, I accidentally kicked my hollow core door by my foot and surprised with that result because I made a toe size hole on my door. If you search for "hollow core door repair" from YouTube you can see what I'm telling about. Yes, it's weak. Inner materials are basically processed cardboard papers. So it's not solid and easy to break but also easy to patch. If it was a solid core door, I don't think it made a hole.
If I were you, I wouldn't invest extra money on solid core doors. I'd rather spend that money on furniture or something else.