The main concern when building anything is the foundation and when it comes to home/pro studio recording stations the first and most important piece of hardware is the sound card. Choosing a job specific system or general use system will make the difference between exceptional audio recordings and “good enough” versions. This is where your level of desire and amount of budget will determine the type of audio client you will be able to service. Several popular manufacturers release new versions of audio hardware every year. In some cases they upgrade a model from last year and in other cases they start fresh with a new design and software architecture. Your needs will determine the cost so cross compare prices between manufacturers and look for the best deal. Ultimately there are affordable solutions for those that want to learn how to become an audio engineer.
You should also consider the hardware and software that came with your computer. Audio engineers usually have a custom built system delivered to their studio and these are job specific. For orchestral mock up releases a system might house terabytes of memory just for sample libraries. For a 4 piece garage band you may only need a few gigabytes for storage. Professional systems are often job or field specific and are built specifically for the tasks that are needed to be executed by the audio engineer. This will also be an important factor in the price of these job specific audio recording systems.
At the end of the day there are plenty of resources available at any search engine. Use specific terms to search for what you need. Ask yourself how much you are willing to sacrifice in dollars in order to get a return from clients. If you even have clients. That is the other side of the coin. Just because you purchase expensive tools it doesn’t mean people will be scrambling to hire you. You might take a loss.