I am attempting to read data from a Netzer DS-25 Rotary Encoder and I am struggling to find a place to start. I am under the impression that I can purchase a microcontroller to read the data via a USB connection, but I really have no idea where to start. Any advice would be greatly appreciated.
A link to the hardware in question would be a good start. I don't imagine everyone is familiar with whatever it is. 
Correct, you buy it from Netzer.
It's called the NanoMIC
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Please identify the exact type of encoder you have. The link points to page with multiple options for resolution, interface type, etc.
Hint: when posting links, keep in mind that everything following the "?" is personal tracking information, and should be deleted.
Questions about Arduino code to read SSI or BISS-C encoders comes up fairly often on this forum, and I have yet to see a successful implementation. The digital protocols are described in the generic product guide.
I suggest you get a copy of the Arduino Cookbook and skim it, stop on any section that interests you. When you get through it you will have a basic understanding of Arduino and what it can do. It can do RS485 but I am not sure about SSI or BISS-C .
Both SSI and BISS-C slaves are driven by a master clock so it would be possible to bit-bang it with about any micro. Throughput could become a problem. This link should help: https://biss-interface.com/wp-content/uploads/2024/07/BiSS_C_protocol_D2en.pdf