Should one just get the first available Prius, when ordering, and then get accessories later. This to improve the speed of receiving your car. So if I wanted different tires than comes standard is it better to get in the car in then change or wait and wait?
Accessories...I have never heard of other tires being available. You would have do that somewhere else rather then the dealer. Since the dealers usually order them by package...just pick a package and color...and have a backup in mind (unless you HAVE to HAVE a certain one). Depending on where you live, and how hard it is to get the car...I suggest getting the car. Most of the items on the packages are not that easy to get "added", so try to pick the model you want in the first place. I wanted a Package 6, but they were not getting any, so I took a package 7... and now I love the Navigation! You can always get things like mudflaps, cargo nets, floor mats, bra, etc. on EBAY and thru some of the Priuschat sponsors.
Well dealer-installed accessories are installed when the car arrives so it's just a matter of whether you want them done before you collect or come back and have them installed later.