Setting up a recording studio – choosing an audio interface?

Hello everyone,

I'm currently building a professional recording studio. I have a room available that's approximately 5m x 4.5m.

I have a large desk where I plan to use the monitoring/mixing area. Next to it, I built a solid wooden vocal booth with insulation, creating a small room within a room measuring 1.6 x 1.5 meters.

Now I'm thinking about how to set up the cables and all the hardware. In the vocal booth, I'll have a monitor connected to the PC, a keyboard, and a high-quality condenser microphone.

In the outside studio there is the PC (which I still have to get, probably build myself as cheaply as possible – up to 600€ – and then it will only be used for music production), as well as a keyboard, a microphone to communicate with the person in the vocal booth and studio monitors.

I already own a Tascam 20×20, which I'm very happy with. I was planning on using this for my studio room.

My question now is: what do I do with the microphone in the vocal booth? I could simply connect it to the Tascam 20×20 in the studio using an XLR cable. However, then I wouldn't be able to control the input signal or the headphone volume from within the vocal booth. I'll also be recording alone—without having someone else in the studio.

Therefore, I would have chosen a small interface with only half the inputs for the booth. If I also use a Tascam, for example, the 2×2, can I "link" the two interfaces, or use them simultaneously?

What ideas/approaches do you have?