The reasons why I need to build this are all, because I want to.
And that's all the reason we need to do stuff eh?
I can't recommend an actual shield because I've not used any of them, so unless someone pipes up and says that the X shield is great you'll have to start searching and reading reviews. I will advise against buying stuff from any vendors that don't have good documentation and support. This means most eBay vendors. Personally I'd rather spend $30 for a board from somewhere like Adafruit or Sparkfun that has an active forum and good support (I assume, I've not required it from them) than pay $3 from Foo Bar Electronics and get no support. That's not to say there isn't a $3 vendor with good support, just don't let your wallet do the thinking.
So to get the ball rolling you need the following
Rotary mount - Lazy-susan or other type of thrust bearing. The bigger the better because that reduces the mechanical advantage things such as wind loading will have. Or a small bearing and some form of dolly-wheel support as far from the pivot point as possible.
Azimuth control - Probably a worm gear I think. That will give you a high gearing and unlimited rotation. Can be driven by a DC motor or a stepper. I don't think direct drive is an option because this may get pretty heavy and the inertia will be very high.
Azimuth detection - At the very least you need to have a single detection point so you can resync the device for parking. Say an opto interrupter at the "north" location.
Altitude control - You said linear actuators, good as anything but 180 degrees is not achievable I think as at the ends of travel the three pivot points will be in line (they may even go over centre) and the actuator will be working against the hardware. Also when the pivot points are almost in line (ie at the start or end of travel) the force required is huge compared to that required once the panel is raised a few degrees, this means a lot of stress and larger actuators. Some careful thought needs to be thunk here, unless there's some clever mechanism I've not seen (possible) sticking to ~90% will be much easier, and as I said before all you need anyway.
NOTE: All the above is moot if you use say another worm gear instead of a linear actuator. But a worm gear will be small and thus have very poor mechanical advantage, once again causing a lot of stress and as well no matter how well you make it there will be play and this will manifest as a large movement out at the end of the panel(s) and large shock loading in the wind.
Altitude detection - Not really required I suppose, just limit switches for end of travel in both directions.
Arduino stuff - Arduino Uno, stepper shield, motor shield, LDRs, opto interrupter, limit and control switches, that's probably about it for starters.
Note that this approach is not really scalable, meaning that if you design for one panel you can't just start adding panels. You have to decide now on the max panels that will be needed and design for that number. The difference between a mechanism to handle 1 panel and that for 8 will be huge.
That's all I can think of for now.