looks like a decent start to me...
connect mac - do you really need midi or would you be better with native cv? which DAW are you using? which audio interface? for midi either the mutant brain or befaco midi thing look good to me - for cv - expert sleepers es9 may be the best option - or possibly the bored brain optx (depending on if your audio interface is dc-coupled or has adat i/o)
correct level for audio interface - do you need this? doesn't the Apollo x4 have a pad? if it doesn't or the pad is not enough - then you should be able to reduce the volume using the veils... and go straight from that... if you'd rather use a separate module try passive attenuators 1st (if you decide you still want a dedicated output module, then your clouds will thank you!!) use 1/4"->1/8" cables and not adapters...
headphone output - alm hpo?
Maths - ok it's a great module - download the 'maths illustrated supplement' and work your way through that a few times- it's a great starting point - try to think about why and what it's doing - not just blindly patching... why do you think you need an adsr? if you do feel you need one then maybe the doepfer vcadsr
"some of the best base-level info to remember can be found in Jim's sigfile" @Lugia
Utility modules are the dull polish that makes the shiny modules actually shine!!!
sound sources < sound modifiers < modulation sources < utilities