https://www.youtube.com/watch?v=vyHPk68z1BEI used Mixcraft recording software using a Yamaha P85 as a controller. What is the most important thing I need when I upgrade my computer? A great soundcard? A new midi controller such as a Korg M50? Recording software?
That is a very broad question. Assuming your upgrading to quad core (PC) or Macs latest greatest then software is a personal choice. Midi controller is the same. It's just a controller. For me my biggest bang for the buck was getting a GOOD soundcard with good Mastering grade 24-bit/192kHz A/D converters. Made a huge difference in my quality of recording. Now if it could help me mix. LOL