Read please my topic named historical infos or something...(i dun remember now!)
There ull find quite interesting things on hun realism.

As to the koku cost, well.
In the solo game u first have to contact port/dutch
then u have to build a trading post
then u can levy teppos.

In multiplayer, all u have to do is get those 175koku together....quite too easy i think.

I am playing a shimazu game and am trying a new technique i encourage all of you to try.
When levying troops, just levy 1 samurai and 2 ashigaru units.
Keep this the same wherever u go.
U can levy any number of ashi, but in any place u train, the ashi under training must be double in number than samurais.

U ll notice two things:
1) armies cost cheap and big numbers.
2) battles start getting really really...REAL and if u make a mistake ure doomed.

Here come the tactics

Now try and let me know.
Remember, 1 sam, 2 ashis, 1 sam, 2 ashis and so on.
Focus on technology and u will definitely have lotta fun!