9-speed Sora w/discs to 11-speed 105 - What Sora bits can I keep? I'm planning to upgrade from 9 to 11 speed, Sora 3500 to 105 5800.

I'd like to keep my existing mechanical disc brakes, which I believe I can, but please correct me if wrong.

Also, if I bought the full 105 groupset with rim brakes (cheaper than set with hydraulics) and just sold the brakes, would everything else still work on my bike with disc brakes?

Lastly, other than brakes, what can I get away with not replacing.  Bottom bracket, shifters, crankset, FD?  Thanks.
You'll need:


A Shimano 10 speed mountain/ 11 speed road rear derailleur
A Shimano 11 speed road front derailleur (since they apparently work differently than normal ones)
Shimano 105 shifters (Front and rear; given the cost of a new FD and the resale plan, you don't really want to reuse the old one + the old front shifter)
11 speed chain
A freehub on your rear wheel which can take a 11 speed cassette
A 11 speed cassette


The brakes will work fine. If you do replace the crankset, you'll likely need to replace the bottom bracket as well. The crankset should work, but it might not be optimal -- on SRAM, the chainrings have been spaced slightly wider apart on 11 speed and the chainrings are likely a bit thinner than 9 speed, which may be the case with Shimano as well.