Looking from a (very) basic perspective: With Ableton and a Mac-Book your studio is complete. You have thousands of instruments and sound-samples, audio and midi effects, you can use your Mac-book keyboard for midi-input, you have a recording device with the built in microphone on the Mac-book and you can use the Mac-book speakers to hear what is recorded and produced. You can record with the built in Microphone a whole band / choir / orchestra in one time, or each instrument / voice on a separate track, by making one separate recording per instrument / voice.
But the technical performance of the sound-card in a laptop or PC is limited, and the number of settings you can adjust is very low.
It makes sense to improve this by connecting an audio-interface to your laptop / PC. You can select then in the Ableton preference settings the audio interface as audio input and output (assuming you selected a audio interface with the possibility to connect speakers or an amplifier). If the audio interface you connected has a MIDI input you can also also set the preference settings from Ableton selecting the audio-interface as Midi-input.
To make a choice between the almost unlimited choice of audio-interfaces you have to look forward on what kind of recordings you want to perform. When you only want to connect 2 microphones ad no midi and you do not want to use it as amplifier for output (or maybe just a headphone) you can find an audio-interface for Euro 150.
I see myself in the future record a band or choir, so I need one with at least 18 channels. I also want to connect in the future good speakers, so I should limit my choice to an audio interface with a built in amplifier with enough power. I have a Yamaha Midi keyboard so my audio interface must have midi in- and output. I want to be able to connect more headphones for the players / singers. I want the possibilty to talk to the musicians, via their headphones without disrupting the recording so my audio interface must have talk-back functionality.
Long story short: I bought the Focusrite Scarlett 18i20 3rd generation.
Functions:
Mic channel input : 8
Instrument Inputs: 2
Line Ins: 8
Line Outs: 10
Headphone Outs: 2
ADAT (simulation of the 8 track tape)
Air
Loopback
Summarised this is 18 in and 20 out.
Now it stands on my piano. Looking at all those empty sockets to plug in mics, it is time to buy microphones. I wait with that until I can get some advice of one of the teachers at Wisseloord.