You need a network shield, configure your modem for port forwarding, put in your details for your arduino. The tricky part comes next.
Create a web server or write an app.
Both methods have pro's and cons, the webserver way will quickly exhaust your resources, memory, you also have to worry about anyone accessing it and then waste more resources protecting it.
The app way would mean a much easier way arduino side, easier to write arduino side if you use an app. . But the down side is without a webpage, it's going to be tricky to remote control on any device without an app.
If your skin resistance is low enough, sweaty etc... or immersed in a water solution of salt or eroded copper flakes, you can feel a tingle even more so with an open wound... just from 12v!
But (and please don't try it)
Stick 240v into bucket of water, spread the wires apart and then stick your hand in, you should be safe as the current will always flow where the least resistive path, place both hands in and the current will flow up your arm then through your chest (ciao, see you at your funeral) down through your other arm and hand..
There's an exception, you can use high frequency with 240ac called the skin effect which makes it safe ...
So current kills not voltage, static produces thousands of volts.
That's the whole point of an LDO, basically as you said in order to sustain 5v you need a little extra head room normal regs require an extra couple of volts, for example a 6v lantern battery pass it through a 7805 and you will get around 4v the solution would be to use an LDO like the one from jameco.
Otherwise finding a 7v source may be tricky and most woluld supply 9v... but now we start talking about heat waste, dissipating the excess voltage to supply 5v.
A switching regulator is usally the best alternative unless you need a very clean voltage supply with as little ripple as possible.
Using just 2n2222s and a 68ohm resistor on each of the base pin, it pulls just under 2 amps when cold.... and sadly even when warm, it still pulls around 2amps! - i've only had it running for about an hour tops so hopefully it gets brighter as it gets hotter lol (68ohm resistors to the base, and no current limiting resistor either on the emitter or collector, they are all sinked via an NPN)
This was simply a test to see what happens if you supply rougly 120ma to each RGB segment of the LED and when it got hot, would it rise to say 200 or even 300ma?... sadly not and if did, it has 200ma of leeway.
either way, it's damn bright for 20watts and hopefully Mr Grumpy is right about high powered LEDs increasing in current when hot because it'll only get brighter and stay well within the 800ma spec limit of the 2n2222's .
I figured it's kinda pointless seeing it in daylight... so I just switched it on (it's 1am, plenty dark enough i suspect)
oh and just to explain... I'm using 2n2222's and no "current regulation" each npn can deliver around 800ma, so I use a 68 ohm resistor to the base pin for each segment, this rougly supplies 120ma per color which is well within spec of the transistor... I purposely kept it low knowing that when the LED heats up, i expected the current to rise up to 200 maybe 300ma, in which case it's well within spec of the 800ma limit of the transistor AND within the 300ma per RGB channels from the 10 watt.
So, 120ma * 3 * 5 = 1.8amps or 21watts.
The multimeter reads 1.8 - 1.9 amps...
Now, because I have no current limiting resistor on the emitter/collector side of the LED, it relies just on the 68ohm resistor, I originally was going to use something like a 30-40ohm resistor and 1/4watt was not up to the job, so i stuck with the 68 ohm resistor and *hoped* that once the LED's warmed up, it would draw more current to get to the 300ma mark.
And (as I suspected) ... No.
The heatsink keeps the LED's cool and sadly (even in 45c / 100f+) heat, still no... maybe if i run it for a few hours instead of 30 - 40 minutes the current will slowly creep up? - good because I like bright.
next time i'll use 1/2watt resistors and push the 50watt boundy, as it is 21watts is bright enough.
Over the weekend, I finally got around to finishing a similar thing, except i used 5 of them... potentially it can supply over 50 watts of light but I decided to limit the current, it pulls around 2amps at 12v (or 24watts) and decided that's bright enough.
But i also did what you did using an attiny85 for the bedroom, they certainly beat 5mm LED mood lights you get from shops..