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Buck Converter for Parallel LED's Answered

So I am trying to make a gift for someone that will include about 100 LEDs. These LEDs have a forward voltage of 1.8-2.2 ( I am going with 2V) and a max continuous forward current of 30mA. The LEDs:

http://www.ebay.com/itm/50-10mm-10000mcd-LED-Lamp-Ultra-Bright-Red-Light-DIY-New-/180763201504?pt=LH_DefaultDomain_0&hash=item2a16538fe0

Now, I want to be able to plug this sign into a wall so I have purchased an AC to DC power adapter that plugs in into a standard 120V AC outlet and supplies 12V with 2A of current. Here it is:
http://www.ebay.com/itm/261176168283

I know one way I could make this work is to have multiple series of 6 LEDs, as 6 LEDs in a series would then require 12V. However, it would make this project a LOT easier to have all the LEDs in a parallel circuit, so I can connect one whole side to the positive terminal and one whole side to the negative terminal. I wanted to know if I could do this: Plug the two wires (+ and -) going from the AC to DC adaptor into a Buck Converter set to 2V and wire it to all the LED's via one wire to a bus wire connected to all of the LEDs' negative terminals and same for the positive terminals.

The converter I was looking at:

Also, if I place the switch in between the AC to DC power adapter and the buck converter, the converter would only be on when the LED's are on, right? Lastly, would all the LEDs have the same brightness?

I know at 2V with 100 LEDs the output would need to be about 3A. Is it okay given that the power adapter supplies 2A but at a higher voltage? As in does the converter convert the electricity to a lower voltage but a higher current?

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