Which motor shield and motor should I run?

I am building a timelapse slider, like a lot of people are, but I feel my gear may be a bit heavier than typical. My max weight of gear is just shy of 8 pounds, and if possible I'd like to be able to move either completely vertical or close to it. I have seen 76 oz and 12x oz motors I believe, but I just need to figure out what I "need".

I have a 1000mm (~40inch) rail that will be powered by the stepper with a GT2 pulley/belt system using a V-Slot rail and carriage setup. I will have 2 ball head tripods allowing for angle adjustments on the fly, as well as using only 1 tripod to gain steeper angles.

I saw a calculator linked here but it need an IPM value, which I have no idea how to find or what is a good value to use if it is something of choice. I plan to use this for video sliding as well (no audio) so I need a constant motion as well as a step/shoot/step mode.

I planned on the arduino shield, and whichever stepper is advised but if I can save a couple dollars and/or save a headache I am open to that for sure. I will be back for code help as I am just getting started but I have found some sketches that may work for me to start. Thanks guys!

8 pounds? Sounds heavy. No idea what size motor for that, my guess would be something that needs more than the 1Amp that normal L293 or L298 shields can control. Maybe take a look at some of the motor controllers that pololu offers: http://www.pololu.com/category/11/brushed-dc-motor-drivers

Ya, it's a DSLR w/ battery grip and telephoto lens. That said, I may never use the telephoto lens and the rest of my gear is fairly light weight. Overbuilding may be worse than dealing with the lack of being able to lift vertically. I don't know if I will use the larger lens, especially vertical.

It looks like as long as I stay under 3amp, btw 4.5 an 13.5 volt, I can use whichever stepper I come across. Is that correct?

The motor linked said that its Rated Voltage is 4.2 volts, which I imagine could be run a bit higher? This is the stuff that confuses me haha. I'll figure out the sketch more than likely, but buying parts is always a bit nerve racking.

I'm watch & see what folks with more motor experience have to say. I've not done a lot on the electro-mechanical side of things.

Thanks for taking time out to respond! I've got the Arduino and hardware coming in so I just need to clear these things up.