Sounds like your are set to go. Things I have found out, take them for what they are worth to you and your situation.
Battery powered mac is a great upgrade to sound. I have to turn my mac's back in frequently and have only been able to use one at home with an upgraded power cord.
Invest in a dual head usb cable, I have found most to be much better separating power and data
I like SS drives for things used a lot, but have never found one big enough for my music. Depending on where you are at on music size, you may want to invest in an external 4 TB or so. I have two drives, one for music and videos and one that backs it up incase the bad angles get it...I have noticed that firewire or lightning is somewhat different sounding... I can't explain it..
Both my hard drives run on battery too, Dave at Pi Audio sent me some cords for it. Its nice when the power goes out and everything still runs.
I have used Audirvana regular, Pure Music and J River. I have heard good things about a new one coming from dB Audio Labs.. not out yet I think. Audirvana was the easies for me to use straight from iTunes. I like iTunes for its organization, and most of them family has i"stuff" to connect to it. Pure Music was good and I liked J River the best after Trung got me to try it. You don't need iTunes for J River, you just point it to where your music is and play. It is a little more time consuming, but has given me the best sound for sit down sessions. Lots of things in there I still don't know how to use.
I use a iPad or iPhone to the mac mini as a headless unit. Works fine, but sometimes I like to see it on the big screen and bought a long hdmi cable for video.
JP