Individually addressable LED Strip lights
OK, that site has really misled you in terms of wire sizes.  Wires have capacity based on amperes not watts.  That means a 14AWG cable can carry 3600W in a 240V circuit, but only 75W in a 5V circuit.   Both are 15A, which is the statutory maximum for 14AWG wire.  Similarly 12AWG maxes at 20A, and 10AWG maxes at 10A.  8AWG is 40A. 

However, your limiting factor will actually be voltage drop.  Because there are microcontrollers in the strip, you need to - if I recall my TTL spec, it's +/- 5%, so 4.75-5.25V. That means you can only have 0.25V voltage drop combining all the voltage drops together, including the voltage drop along the strip itself.   Your drawings show feeding the strip in a lot of places.  That's the right idea.  With these cheap strips, assuming 0.10V drop down a 1m length of strip is hopeful, so you can tolerate 0.15V of additional drop in the distribution wires. And that's where you'll get nailed.

You need to carry 18A from the power supply to the first strip, 16 feet (except it's round-trip, so 32.)  Let's run the math a bit.  

Try 12AWG wire. 0.0016 ohms per foot.  x 32 = 0.051 ohms = R.  I is 18.   E=IR  E (voltage drop) = 18A * 0.051 ohm = 0.92 V.  Good grief! That won't do!

OK, well suppose we do a 12AWG homerun from each strip to the supply.  I is 3.6.  E=IR 3.6A * 0.051 ohm = 0.184 V drop. gahhh, close enough.  You can bump it to 10AWG if you really want to. 

How about busing with fatter wire?  Rather than iterate, let's work backwards, E is our max tolerable (0.15V), I is 18A. R becomes 0.00833 ohms. The most resistance we can accept is 0.00026 ohms per foot. You don't want to know what wire size that is, but its last name is "KCMil".

... and you thought you were going to use 16AWG... SMH the things you read on the Internet...  and this is why I said the 5V makes it much harder.  If this was 12V, you would not have learned the term "KCMil" today. 

So 


Q1:  Neither one.  Trying to run 18A or 36A down a single bus is doomed to failure, since power loss due to voltage drop is a second order of amperage.  The only thing that is not insane is a separate 12AWG homerun from each 1m strip back to the power supply.  
Q2: 10 or 12 AWG depending on how voltage-drop-tolerant you are.  LOL 16 AWG LOL... I wish you had tried it, I would love to hear how it turned out.  
Q3: In case you haven't figured this out by now, use the number of power supplies that lets you move the power supply as close as possible to the point of use.  
Q3B: You are linking cheap Cheese power supplies, and it's a big mistake to try to run those anywhere near their nameplate rating. They're just not that well built.  If you were using GE supplies, different deal. 
Q4: The control circuit looks reasonable though I might try branching that instead of a big long end-to-end. Don't make it a loop. 
Q5: I would not parallel the power supplies.  That shouldn't be a problem if you do a separate homerun for each 1m strip. 
Q6: If you don't parallel the power supplies, that should make backfeeding impossible, but in any case, don't allow it. 
Q7: unless there's a signal propagation problem, I would want one central control unit, so one Arduino.  You might try having the Arduino on its own supply, or at least power it with a separate homerun.