Shimano 105 to Dura Ace Di2
Greetings,
I want to slowly work my way to Dura Ace Di2 and do not want to upgrade all the pieces at once. I currently have Shimano 105 R7000 and Shimano 105 hydraulic disc brakes. My ultimate goal is to get to Dura Ace Di2 shifting, If not required I would leave the hydraulic disc brakes the way they are. Can anyone provide me advice on what I can switch by itself that is still compatible with the 105s and what must change together, i.e. rear derailleur with electronic shifter. Never done a piece meal upgrade before. Thank you in advance for any assistance.