Nice job!!

Another idea could be as you arleady have made a point for having shipbuilfimg knowledge on the MC is to use 16th-18th century naval ships and trade ships that made the Graet Britaon Empire reality instead of using the Westeros naval forces of galleys and longships. For example sloops and brigs as escort to trade ships, trade galleons a type of a mix naval and trade ship from the Spanish Aramada had more cannons and was more sturdy able to transport a large amount of products contrast to merchant carracks of the time. In addition the carracks needed more escort ships due to lower firepower and defendinv capabilies. Another useful trade type ship is the clipper famous for the lighweight products ot could carry like tea, Coffee anx spices but really fast. On the naval part thrlere are the famous "man o war", in reality is the early frigate ship and it changes its size along with its manouvrability, firepower and crew number on the rates (like 5th, 4th and 3rd rate frigated) after that are the Ships of the Line (1st and 2nd rate onlu doffrence on size) very expensive but they were really breasts on the sea in ther time similar to the now decomisioned battlsehips. I think that you shouldnt for the story plot supersede the age of sail into the age of steam, i mean really tarins and steam ships in Westeros are not very intresting it loses the more realistic asprct of the story. For me the technolgy of the late 1700 is the limit. Its in the late medieval age and early to middle discovery era. So that both land forces an naval battles are not far fetced onto technology but still using tactics starteagy and teh adveseries have similar of lower quality weapons. Like other enemys still have pikes and polearms or bows and swords but they fight in a giant melee where heroics and ist man fights for his own however a welk trained pikemen unit along with a legion and some supposting ranged units can take them out even ig they are aritmerically inferior. That ls my thoughts on it at least hope it hepled and really waiting for your next chapter...

Also some great stories to take ideas from i think are: Deeds Not Words - Fanfiction Dread our wrath - Spacebattles Just Another Si - Fanfiction Sorry i dont remember the authors only the titles. Another suggestion could be an agricultural revolution introducing New crops resistant to the cold climate maybe impoeting them from essos and some new techniques like crop rotation and New Steel plows. That could help increasing the population. Along thise lines you could bring the peasefull wildlings from north of the north, asimmilating to the northenrn society and culture maybe reintroducing the Old Tongue.

Sorry for some typos i am writing from my Phone

Some thoughts. Firstly, congradulations on trying to make a story purely on scince and actual historical facts instead of using magic. I like your touch on the whiteealkers as i strongly believe that usually are used as an existensial threat and non logical really destroyong any good plotline. The ASOIAF universe has so many thinks to explore and do that using a aloen existensial threat like that is really subpar. Now on the reccomendations you ask, i would like to see plans for a road system as although maritime trade is great and good but the North is huge. The Romans built their empire on their abiloty to make roads both for trade and their armies. Secondly i would like to see Some city building like make the Winter Town into a real northern capital Winter city for the Starks, there are many advantages there both millitary, exonomical and cultural. I would also like to see more development on the Northern culture and menatlity in contrast to the Southern Westeros, by using the Old Gods religion (beeing freer than the Seven) maybe Some Kind of Northern Knights or an Order that takes an oath in front of a Heart tree in blood. Culturally uniting the North touches on the propaganda you mentioned in the earlier chapters. Anothe suggestion is building Some Kind of central army loyal to the Starks either a permanent proffesional force or a rotational one (training the levies that way) using ideas from war history from earth like the Roman legions or the Swiss pikemen or the English longbowman or the frensh crossbowmen, Knights as heavy cavarly etc. I wouldnt recommend introducing cannons and gunpowder exept for naval battles, where the range is not bigger than the ballostae by much and the reload time not much diffrent either, keeping the land battles cannons free and using tebuchet instead. More intresting that way and you dont take the castles out of the equation. Thats my suggestions that i thought up.. Hope it hepled. Great story.. And plot maybe check your vocanulary a bit make it more medieval like instead of safe - treasury. A fan