1Smug_Bastard BlackBox: you can log to the built-in memory, but dumping the log through usb is slow. if you need to log high level of data you could purchase either openlog SDCard reader or better openlagger (which is mlyle beefed-up version of openlog). Note however that autotune logs the aircraft behaviour and prior to applying tunes values, you can see in a graph oscilation and noise on each axis, which makes additional logging pretty useless.
Seppuku & BrainRE1 OSDs are fully graphical OSD, other flight controller do only provide "MWOSD like" graphics. In the "Deals & Sales" post @yds compiles a list of fligh-controlers he's successsfully tested with dRonin. So if you can live up with a more simple OSD, you can save a few $.
The Brain RE1 is tight on memory, I don't know if it can cope with the tricopter add-ons. At least you will not be able to use the OSD together with "FullBore" logging to an sdcard.
There is no BEC in the seppuku, you need either a 4in1 ESC with BEC or a power distribution board (the one from Brain and Matek are what most of us do use). Brain mpdb V2 does support 6s, V1 is limited to 4s. Brain mpdb is limited to 1A which is not much considering the servo needs. I would use a small separated ubec for this purpose.