Cortana is a zombie that cannot be killed. Microsoft really wants her to be part of your life, listening to all audio in case you say "hey, Cortana". The good news is that ASIO and WASAPI bypass Cortana, so she's not going to slow you down.
The biggest class of CPU killers are interrupts, which take priority over everything. When a hardware device signals an interrupt, its handler then schedules a Deferred Procedure Call (DPC). You can't easily see interrupt overhead, but you can measure it indirectly by looking at DPC overhead. There's a tool just for this purpose, called
LatencyMon. It's a good place to start, because it'll identify actual problems rather than just blindly stopping services that may or may not be problematic, or that may or may not be necessary.
If LatencyMon reports that your average DPC latency is low enough for audio - and it'll come right out and tell you that - then you're done. If it does indicate a problem, the site offers procedures for tracking down the offending device(s).
The biggest impact on audio performance isn't Windows-related at all, but the processing that goes on within the DAW itself. Some plugins are very CPU-intensive, and some introduce a great deal of latency. Best strategy is to hold off inserting any plugins until tracking is finished, and then bump up audio buffer sizes for the mixing phase. Once you're done recording new tracks, the additional latency of large buffers becomes irrelevant and you can set them as high as your interface driver will allow.