The NUC was used and just cost me a replacement fan. USB audio interface was cheap from online classified. The touchscreen was just over a $100 on AliExpress, plus a bunch of cables of various sizes and angles to connect it all.

I've done the bare minimum to get this all going and haven't done any optimizations. Sampling at 48kHz. Load is about 5-6% even with a complex effects chain. I don't notice any latency, but I haven't measured it. Latency isn't an issue for the experimental instrument I play. The electroduochord.