Are you near an ocean? I trust you never see salted roads in the winter. Unless one of those is true or you sweat a ton, there is not much reason to worry about galvanic corrosion. Use aluminuim parts where they are better and worry about corrosion when it comes up. Greasing stems, seatposts, bolt thretc. is ads, ealways a good idea and doing it with marine grade grease (the stuff for boat trailer hubs; available in any auto parts store, at least in the US) has stopped galvanic corrosion in its tracks for me.

That rack looks marginally stiff. You may find going uphill with weight on it and standing out of the saddle is not fun. We all did exactly that when the Pletcher racks were the standard 50 years ago. Then Blackburn came along and life on bike got a real step better. Lots of good choices now.