I don’t want to clog up the SSD with other stuff, so would like
programs such as iPhoto to use my external USB3 hard drive. Is there a
way to make all programs use the external drive as their default
Not easily by default and if you go the route of symbolic links to essentially relocate your user’s home directory, you run the risk of creating a “Frankensystem” that might break if either drive dies; I don’t recommend that.
But you can set this on a per application basis. For example, in iPhoto you can launch it while holding down the Alt/Option to choose where the iPhoto library should be stored; see pic below. I do this myself not for SSD reasons but because I don’t like my system drive to “bloat up” which makes backups more time consuming.
I don’t want it to start auto-importing the photos from my iPhone to
the SSD when I connect it for example.
Well, this again is another iPhoto specific option. Launch it, go to the “iPhoto > Preferences…” settings and adjust the setting called, “Connecting camera options:” as shown in this screenshot:
My external drive has 2TB of storage space which I’d rather use. I
would also like my audio programs to record the audio to the external
drive, keeping the main program on the SSD. I intend to use Ableton
Live Suite 9.
I am not familiar with the setup specifics of these programs, but pretty much every professional program in the world has some option as to where default/scratch files are saved. For example, you can set where iTunes stores media in the “iTunes > Preferences… > Advanced” settings right under “iTunes Media folder location” as shown below:
But Apple has made things a bit more “fun” with the integration of iBooks into iTunes; now iBooks related stored has nothing to do with core iTunes storage and it stores your data right in a
~/Library/ path in your user directory like this:
Of course if this is for music production, the chances of iBook storage being an issue is quite slim. But still, Apple is not making it easier to place media storage away from the core system setup.