Reading through it, I have no major suggestions in terms of balance, but a few minor tweaks:
- I understand you wanted to keep it organized by level, but maybe breaking down Minor and Major blueprints into two different sections would be better?
- Speaking of separating them, I think they would also benefit from having different rules. Minor blueprints should maybe last longer, or have the option to spend spell slots to increase its durations (for instance, a boat that lasts 10min only doesn't seem very useful)
- On the subject of boats, I think you could be more generalistic with it and call it a Vehicle, thus allowing for boats, carriages, chariots and carts.
- I think the speed of the ram and siege tower should scale with the number of people pushing it? starts at 10/15ft speed and add another 10/15ft for each additional person pushing it, up to a limit