other little things
You definitely want the aileron trim (manual in my case)
I modified my canopy handle by cutting off the hoop, cutting 5/8" off each end of the hoop, and brazing it back on. This still fits your hand nicely, and keeps the hoop from interfering with the back seat rest when accessing baggage.
Decide now about rear battery or front. If you opt for rear, and change your mind later to front, it is easier than the other way around.
Order a whole bunch of the black plastic bushings for cable pass throughs. The 5/8" ones. Not much use for the little ones, just a few. I used MANY. I even used some 1" ones I found at the local hardware store.
Go with the "Delux" throttle quadrant. The stock one is just not nice enough. I modified my Throttle quadrant mounting cover so it is easier to install and remove, looks more of a natural fit in the airplane. Others have done some significant mod's here -- hand ergonomics is important.
I would not recommend spending the money on the back seat rudder pedals. I'm not alone in buying them and then not installing them. I wish someone would engineer a nice set of rear pedals.
Start thinking about whether or not to modify the fwd baggage bulkhead for instrument bay access. I did not, and I am happy -- I used the bulkhead to mount a bunch of things, which you can't do if it is an access door.
Order a ton of platenuts and install the floor panels with plate nuts. I used every other hole.
You might consider the rear-baggage shelf modification that Mike Robbins did to his - you can gain a huge amount of storage space. See this:
http://www.romeolima.com/RV8/MikeRobbins.htm
The little center box is for the elevator bellcrank.
You can do this even if you put the battery in the back, it just means that the center box is somewhat bigger. I wish I did this now. But doing it to a finished airplane is more work, less fun.
If you think you might use the Classic Aero Designs Aviator seats, then delete the standard front seat back. The Aviator seat has the seat back built in. On the other hand, I modified my stock seat back to be comfortable to use with a parachute, so I have both. So you might decide to keep the stock one too.
Lots more options come up with the finishing kit.