I made a thread a while back where I introduced a sizing calculator for turbos. I've made countless tweaks to it and I'm finally happy with it. This calculator works for compounds, parallel twins, or staged twins. You just have to take a little time to see how to use it for configurations that are uncommon. I've also added all the compressor maps I've collected and made them available to you all. I hope this will be useful to you.
I've updated my calculator to fine-tune the fuel requirement section and I've probably made a couple other little tweaks over time, but I can't remember for sure... It now includes output to size your injection pump / unit injectors and your lift pump.