Automated Video Slider with Pan/Tilt Head - Hardware Design

In my approach to hardware design I will rely on the affordable off-the-shelf components.  Some of those components (slider or head) I already own.
Disclaimer 1: I am neither electrical nor mechanical engineer and I learn as I go.  And I love it!  I make mistakes and some of my statements could be wrong.  Feel free to correct me!
Disclaimer 2: This is a work in progress.  I think it should work.  But it might be proven to be otherwise.

Pan/Tilt Head

Instead of building a pant/tilt head from scratch (which is totally an option, given that I do not need tilt that much! well, maybe later), I will use Bescor MP-101.  It is almost affordable (I've got a used one for $80), adequately silent, and can be controlled externally, using Arduino's PWM outputs.  The head can be powered by 4xAA batteries, but external power connector is also available.  I intend to use the latter.
Parts:

• Connect head to the controller using 7-pin DIN cable.
• Power connector?? 5.5mm x 2.1mm?

Here are few sources related to use of this PT-head as a platform for application development:

• Chocolate Factory Pan Tilt USB Hack
• Bescor MP-101 Hack
• Bescor MP-101 Wireless Bluetooth Controller
• CamRanger PT Hub
• StackShot and CamRanger
• USB Pan Tilt Controller with Sony LANC (S-Link) interface

Slider

I already own a cheapo slider from Craigslist, which looks something like this.  EDIT: Found it!  This is Glide Gear DEV 1000.  For now this should do it.  I intend to motorize it.  I suspect a (cheap) stepper motor will be too jerky and/or loud which is not good for video shooting.  Therefore I decided to go with a DC motor. This also means that the position of the carriage will be unknown and its movement speed will be hard(er) to control.
Parts:

• 12V DC gearmotor 12RPM. Shaft 4mm
• Motor mount - to be designed.
• GT2 timing belt (6mm wide) with pulleys (20-tooth, 5mm bore).
• 15-tooth, 5mm bore pulley for GT2 timing belt
• TB6612FNG motor driver, datasheet, sample.
• 2x Endstop Switch.

Controller With Display and Keyboard

Parts:

• Arduino Mega2560 R3.  I decided to go with Mega as opposed to Uno because price difference is negligible and I do not mind extra size.  Room for growth is always nice!  However if all you want is to control the Bescor head alone, Arduino Uno should suffice.
• Proto Shield.  I plan to use this space for slider motor driver.  Maybe other parts.
• I strongly believe in the need for appliances to have GUI. This seem like a no-brainier:  Keypad LCD 1602 shield.  I wish the keys were arranged better and the reset button was less prominent.  Alternatively maybe 20x4 LCD display paired with Nunchuck with WiiChuck adapter would be a better option?  For now I will stick with the 16x2 LCD/keypad shield and will just rip the reset button and the power LED - it is way too distracting for my comfort.
• Connect to WiFi via ESP8266.  For now let's just leave it at that.

Power

I need 12V to drive slider motor - adjust the voltage to make sure sliding is slow enough.  6V to drive the Bescor PT head - adjust the voltage to make sure the panning is slow enough.  7V to drive Arduino and 3.3V to drive WiFi board.  I think 12V, 5A DC should be more than adequate and 5.5mm x 2.5mm power connector will do the job.  This remains to be proven though.
Parts:

• 12V 5A AC power supply connected to controller via
• 5.5mm X 2.5mm DC power supply socket.
• For powering the PT head or even Arduino I might use this DC-DC step-down module.
• Battery power.  I can go with a cheap 12V battery pack.  Alternatively Sony NP-Fxxx compatible batteries are readily available and, most importantly, I already own a few to power LED lights.  In this case I will also need a plate and DC-DC voltage booster.

That's it folks!