Bread dough. Rookie questions I am trying to make a multigrain/white blended bread, I want to break away from using a breadmaker and manually mix it. 

My recipe:


  
  1 package (1/4 ounce - 1.5us tsp) active dry yeast (my previous attempts did not rise very much, suspected old yeast - new yeast was purchased, confirmed active)
  2-1/4 cups warm water (110° to 115°) (water verified this temperature range with thermometer before mixing begins. any extra added is less than 15ml and also the same temp)
  3 tablespoons sugar
  2 tsp salt
  2 tablespoons butter
  6-1/4 to 6-3/4 cups flour (using 2 cups of multigrain bread flour, 4 cups all purpose white flour)
  


procedure:


  Yeast is activated and dissolved in sugar water mixture before other ingredients are added. After adding, as per the above recipe I knead it for 10 minutes on a floured surface. Initial rising time is 30-45 mins or until doubled, dough is punched down and then shaped into loaves and divided into lightly greased breadpans. secondary rising time 30 mins or until doubled, placed into 350F oven for 30-40 mins or until lightly browned bread sounds 'hollow' when tapped.


Questions: 


What should the dough look/feel like when it's ready? (can anyone post me a picture of the targeted product?) 
What is overkneading? 
Is the recipe alright? 
Do you have additional steps to follow? 


My background: I am a 260lb x-military veteran who regularly does 1000 pushups every 3 days, avg bench is 300lbs for several full sets, overhead press and pulls are roughly the same weights. 

The point of me saying this - someone suggested I have kneaded the bread too much and too strongly.

Previous loaves were hard and did not rise very much.

Please offer this rookie some advice.
There can be a lot of things happening here, but I will start with some first ideas. 


You are not overkneading. Overkneading is not about raw strength. It doesn't happen per hand, not in 10 minutes (actually, it doesn't happen in the mixer within 10 minutes either). Whatever your problems are, overkneading is very unlikely to be one of them. If it were, you would notice a pronounced change from sticky through supple to weirdly-noncohesive. 
You are killing most of your yeast off. 110 to 115 F is not "warm" water when it comes to yeast, it is scalding. If you absolutely need quick rising times, use water at 90 F, +-5. Room temperature water (70 F +-10) will produce better tasting bread, and also has a larger margin for error. 
Forget the time directions for rising and really go with "until doubled". Proof in a measuring container, or at least in a square or cylindrical one where you can mark the initial level. "Just kinda stopped" should not happen before doubling, if the yeast is well and alive. 
The problem is not in the proportions of your recipe. They are pretty much middle of the road, assuming that you are really following them and not mismeasuring somehow. If you think it is a measuring issue, weigh the ingredients, that's not nearly as error-prone as baking by volume.  
A somewhat far-fetched idea would be that you beat too much flour from the mat into the dough during kneading. My quick calculation shows that you would have to beat in well over 150 g of flour before it starts getting unpleasantly hard, but if you want to avoid this source of error, knead without additional flour (just disregard the sticking).
Preheat your oven. If you have a pizza stone or some other good thermal mass, use it.  
If you really have that big problems, try simple white bread first. After you have mastered that, you can get to multigrain loaves. They typically don't rise as much as white bread, and are more difficult to get right.