First of all, you have to start from clearly defining the purpose of this studio. If it's just about producing some instrumental songs, you need a certain set up that excludes the voice recording part. If it is a band with musical instruments, it is more difficult because the sound card must have several inputs (for live sessions without overlaps) and there is the problem of space for all instrumentalists (especially for the drummer). If the purpose of this studio is clear, is better to make a list of everything you need for that studio and it should start with the strictly necessary equipment after which you can make the purchases step by step.
Here is a list of the necessary:
BASIC STUDIO - with this configuration you can already make instrumental songs using only a synthesizer or plugins from your computer
Computer - it can be a laptop or a desktop but with a good configuration and you need a professional music software (you find a lot of options on the market)
Audio interface - the number of inputs and outputs must be chosen according to the number of artists who must do the record all together
Keyboard - it could be a workstation keyboard synthesizer that has a midi interface (in which case the sound card must have MIDI input) or it could be a MIDI keyboard that can usually be connected directly to the computer via USB
A pair of headphones - they are useful for mixing or mastering in the absence of studio monitors and also when you are working on a material at a time when you may be bothering others (in the middle of the night)
Studio monitors - they are useful for mixing or mastering and also in live recording sessions with instruments that do not require microphones and if you have those monitors you can get rid of the use of headphones and splitters
RECORDING OF LIVE INSTRUMENTS
Cables for connecting instruments that have outputs - the compatibility between the outputs of the instruments and the inputs of the sound card must be checked (cable type jack / XLR and signal level)
Microphone for instruments without cable outputs - if you choose the condenser type you need the sound card to supply +48V (phantom power)
if you have more instruments you will need more microphones, headphones and possibly a splitter for the headphones
if you do not have enough inputs in the sound card with phantom power you will need Active DI Box or preamp with phantom power
RECORDING A VOICE
Large Diaphragm Microphone - there are many models and brands on the market and prices start from a few hundred and rise to a few thousand pounds
Pop filter (pop shield or pop screen) It serves to reduce or eliminate popping sounds caused by the mechanical impact of fast-moving air on the microphone during recorded speech and singing
Compressor - It is very important to use a compressor between the microphone and the sound card because it may exceed the input level in the sound card and they may give distortions impossible to repair after recording