i would say, determine how long of strings you need, then buy them is chucks as you can afford...
then put them away, or play with them, but don't set them outside yet.
if it takes 2, or even 3 years, so be it.
then when you have all the items, then set it up then. you have what you wanted and didn't break the bank.
the nodes are very reliable now.
also along the way, pickup the hardware too, like grabbing a 16port active hub, and a 16port passive hub. (most people are going above 16 strings nowadays, plus it gives you room to balance power. Build your ssc's with the two wires to come out of the bottom cap. this really keeps the water out (especially if you bind your ssc to the rope, or wire or tube that holds your strings to the tree.
the battery boxes are wonderful for storing the hub and power supply. (i'd suggest keeping each hub in its own box to make it easy to service or swap out.)
if you buy you're stranded cat5 cables (like at monoprice) pick a different color cable for the wires that go from the hub to the ssc's (as opposed to the dmx wire, or the pixelnet wire from hub to hub) so that when you do make a switch, it's really easy to not screw up.