Hey Zener -
Thanks for the post! Yea, I haven't begun laying it out yet, but I'm sure I'll have million questions once I do. I did see that you can force mono mode on the si4735 by setting the fm blend mono threshold level (pg 23 and 28 on the data sheet for the si4735), so I guess leaving the R output floating and connecting my coupling cap to the L out only would work then.
In the Sparkfun shield Vdd and Vio on the radio were connected to a digital pin (8) on the mcu via the hex converter (which I've omitted because I'm using a 3.3V atmega board); is there a problem trying the radio directly to power with the proper filtering caps like I have in the schematic?
Also, do you have any specific recommendations for layout, or the FM antenna section of the board?