The 2i2 was the top reccy for an interface a couple of years ago. I was never quite sure why? That Shure 87 is a "back electret" capacitor mic but intended for close vocal work like a dynamic hence its sensitivity is very modest at 2mV (Pa) which is only about 4dB hotter than a 58. I can assure you the M4 will be fine with it or even a 57/58 at sensible distances, say 6" for vocals, 12" for strummed guitar. However, the early electret mics did not age well so it might have lost a lot of its output.Ooof, that’s a little too close to the chest. I’d spin my wheels another 6 months because I need everything “perfect.” Sound advice to just begin and learn on what I have.
Tbh, it isn’t my first foray into recording—I started with an old tape recorder > a “mini disk” tascam > an mbox mini w/ a chronic crashing protools > and at present I (admittedly) have a 2nd gen Scarlet 2i2 that has two line outputs that I use with audacity. I have a shure 87a (?) microphone a pastor gave me years ago.
The idea to start over came recently when looking at additional microphones.
I am thinking (hoping) one of these interfaces is a step up from the Scarlet in terms of preamps, ins and outs. Truthfully, I’m just not impressed with the scarlet.
Why do you want to record with 3 mics friend? You could, with the M4, use an external preamp and feed it into inputs 3/4. However, at this early stage look for a second hand mixer such as a Behringer Xenyx, Soundcraft notepad of a smallAllen &Heath. They will give you two extra mic channels and the ability to select various line sources such as CD player. synth. But, I suggest you nail the basics first.
Dave.