I was looking through your original list of options parts, and noticed one item you should update. The 355100 Active Diff is for the original XB8 to the EC, but not for the 808. The part number you want for the 808 Active Diff is 355102. This system will include the correct 43T ring gear and shorter outdrives for the 808. You could convert ta 355100 to work with the 808, but you will need the 355143 ring gear and 808 specific Active Diff outdrives (I will have to get the part number at work tomorrow). The cost of those pieces would not make a conversion justifiable, unless you have an Active Diff already.
The 352303 and 353303 offer some added adjustability to the suspension, but if you are just starting out, you may want to leave the stock pieces until you get comfortable with the car and are ready to tweak the setup to your driving. The optional plates do look fantastic, and they are a bit easier to deal with when you want to service the diffs. If you install them, you may just want to start with the equivalent to stock geometry unless you feel the setup needs some work. The same holds true for the steering plate, 252573. The stock plate is quite durable, so your main benefit would be to fine tune the aggressiveness of the steering. XRAY tried to simplify the stock pieces so that the setup was not overwhelming to most users. Durability of the stock parts is great, as many have commented on, and most of the options add some added tuning benefit(hinge pin holders, chassis braces, etc.). Having said that, man do the aluminum caster blocks look trick! I didn't plan to use them for mine, but after seeing the press release photos for them, I may have to get a set just for appearance! They are one of the coolest 'looking' options XRAY had produced!
As many 808 drivers have shared with us, only a couple of spring sets and oil weights to adjust the shock and diff package is all that is necessary to get the car close for most drivers and track conditions. Tires and the shock package are probably the most critical "option" pieces to get your car dialed in. When you start to fine tune the setup, these option pieces give you an added range of adjustment. I am a sucker for options, so I will probably add many of those same pieces to my conversion too, but my 808 is a much better car than I am a driver in its stock form!
Bryan