I'd say start with whatever comes in first. Depending on your budget, you might be ordering in chunks versus all at once. My experience has been that the soft parts take the longest from order to delivery (due largely to the fact they're made to order based on measurements you provide). The armor, gauntlets, helmet, etc. usually have less time from order to delivery, but check with the vendors as that varies based on season (sometimes too cold or too hot slows them down). Boots and gloves seem to be the hardest to track down recently. Most of the build threads on here are 501st approval level, so you should be pretty good to look through some of those, many of which have part and vendor lists at the top.
