Question: I know a lot of posts have been made on this topic, but, I have tried everything. I wanted to move my hot water tank from the first floor of my house to the crawl space. My old unit was performing well, but, the plumber I hired recommended a new unit (mine was 12 years old). Prior to replacement, my hot water worked perfectly!! We could take three showers back to back with no issues at all. Now, with a new unit, I can't even make it through one shower before it gets cold. During the one shower, I constantly turn the hot know to increase the temp until it just gets cold on me. I have taken the following steps:

* Replaced the new HW unit with the same size (38 gallons), number of elements (2), and wattage as the old unit
* Checked the dip tube in the new unit
* Replaced the elements (with genuine factory parts)
* Adjusted the thermostat to 120
* Replaced all the stems in faucets with a one handle (mixing stems).

I have already dropped 1500 dollars on the unit and stems including labor costs. Please advise.

Answer: 
If you increase the diameter of the branch you also increase the time it takes for you to get hot water. In my climate I also like to get ground temperature water so having large branch lines increases the amount of water I have to dump before I get rid of the water in the pipe from the supply entrance to my faucet. This also wastes heat as the branch lines will have hot/cold water and heat or cool the wall spaces - eventually heating or cooling your house. 

I like the manifold arrangement but one quick thing to try would be to just plumb the washing machine into the end of the branch line. I this this would allow the other fixtures to have pressure preference over it. 

The other thing I'd do is eliminate the crazy 90s if you are redoing a section. The plumbing might look neat but you loose significant flow when you make sharp turns. Really the best way is spaghetti with gradual bends.
If the manifold cost is not exorbitant, I would definitely go with your plan. I can hardly believe that anyone would use a 1/2" line for a trunk. I'd be tempted to use a 1" trunk if you have the crimp tool or can borrow one--especially to feed the manifolds (and your incoming line is 1" or larger).