Troop production and feeders

Assumptions:
1) Gold bonus for resources is assumed; Therefore every village produces 1250/1250/1250, or a total of 3750 resources/hr, meaning a feeder produces 3750x24=90,000 resources per day.
2) I will use wood/clay/iron costs and wood/clay/iron production only
3) I assume that you either NPC your resources to the proper balance, or that you trade on the market for resources you need.
4) All buildings are assumed to be level 20.

Let's start with Teutons:
Axemen
Cost: 130+120+170=420
Build time: 3:23
Can build in one day: ~450
Resources required for barracks working 24/7: 450x420= 189,000 resources per day.
Feeders needed: 189,000/90,000= 2.1
Feeders needed for the GB: 6.3

Teutonic Knights
Cost: 450+515+480=1445
Build time: 8:20
Can build in one day: ~170
Resources required for stable working 24/7: 1445x170=245,650
Feeders needed: 2.7
Feeders needed for GS: 8.1

So as a teuton, to keep your barracks, great barracks, stable and great stable building non-stop, you would need 19.2 feeders. Not quite as many as people assumed. To keep a barracks/stable combo going non-stop, you only need 4.8 feeders. Everything after your 5th is extra resources for great barracks or workshop, which I can work into this later on.

I will do Gauls and Romans tomorrow

At this rate, you can amass a respectable 8k/2k hammer in less than 2.5 weeks, using only barracks/stable, and a little over a week using all four.
I hope these numbers illustrate that building a respectable hammer is not wildly expensive, doesn't take forever and is quite feasible, especially for Teutons. As you will see later, Roman/Gaul hammers are slightly more expensive.

Romans: (courtesy of d-_-b)

Imperian
Cost: 150+160+210=520
Build time: 5:24
Can build in one day: ~275
Resources required for barracks working 24/7: 520x275= 143,000 resources per day.
Feeders needed: 143,000/90,000= 1.58
Feeders needed for the GB: 4.76

Equites Caesaris
Cost: 550+640+800=1990
Build time: 9:57
Can build in one day: ~150
Resources required for stable working 24/7: 1990x150=298,500
Feeders needed: 3.32
Feeders needed for GS: 9.95

So as a roman, to keep your barracks, great barracks, stable and great stable building non-stop, you would need 19.61 feeders. Not quite as many as people assumed. To keep a barracks/stable combo going non-stop, you only need 4.9 feeders. Everything after your 5th is extra resources.