....10ebbor, I have to ask: Where the heck do you get all this obscure knowledge from 
No idea, actually. Tendency to remember stuff I read. (Mostly the nonimportant parts, but anyway)
I have that as well, but tend to focus more on natural sciences and earlier history. (Which is part of why everyone else is so much better at naming specific historical precedent than I.)
Anyways, I will just repeat some things that were already said in some form or another that I agree with:
1. We should set up the town wall fairly soon, although with plenty of room to grow.
2. Our tower should have multiple purposes.
3. Our fortifications of all sorts should be capable of protecting all valuable things we have, most notably our citizens.
4. We probably shouldn't start just yet, just plan and see if we can find workers.
5. Careful about passing a keep off as a tower.
Now for something not said: Gervassen, your research is pretty impressive.