I have easyflash, jiffydos and sd card reader on my c64 now
Here is a photo of my Commodore 64 I just snapped. I am particularly proud of the little 1541 sticker I made for the built in SD card reader [Another example of my very limited electronics experience lol.. pop in a board, find a way to mount it.. connect it up and go. After all these years, I am decent at soldering and de-soldering at least.]
Nice, I like the sticker. Yep, who would have thought back in the days that you could integrate a 1541 floppy drive, and thousands of disks, into the C64?
The EasyFlash 3 is a good device (my Kerberos cartridge emulates EasyFlash 1, too, so you can play Prince of Persia from CSDb with it, a very good C64 port). With the USB port of the EasyFlash 3 you can upload programs direct to the C64, good for cross compiling on a PC and fast testing on the real machine. That's very useful if you want to test some DIY hardware attached to it, or special SID features which the emulators can't do. It's crazy what you can do with the SID. Do you know this demo? Only recently VICE has been updated to play it correctly.
It sounds awesome, like an Amiga. But some of the magic of the simple SID sounds is lost with these new digi tricks.
Have fun with your SID-Arduino-MIDI project. If you have a good keyboard with knobs and wheels, maybe map the SID filters to the knobs and the wheel to the pitch, implement some C64 style effects like arpeggio, and then play some music
Or write your own tracker on the Arduino and then write some music for it or port some of the old musics. One of my all time favorites is the Tetris music (no, not the annoying Gameboy music)