you can use your audio interface, the appropriate cables, probably some amplification* and possibly attenuation or an output module - I can't remember if those focusrite interfaces have balanced inputs or not - but if they do or your power is unbalanced - then a balanced output module is probably a good idea
*for amplification you could use an input module - or if you are not going to use it constantly something like MI Veils is a good buy as it has a lot of gain available, is 4 channels and is a cascading vca so can be used as a mixer - intellijel quad also does this - not many vcas do!
not sure about midi as I don't really use it that much in that way - sometimes I use cv to midi cc for controlling a video synth, but not often
but if you want midi i/o from the modular then befaco make both in and output 4 channel midi modules and are usually pretty good
"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