SPFx and some npm packages has been updated so if you have used my previous post http://www.dunite.se/2017/12/25/aurelia-spfx/ on Auerlia-SPFx make sure you read this.
It is important to verify your version of Node and NPM. These version dependencies are related to SPFx and not to Aurelia it-self.
npm --v 5.6.0 node -v v8.11.3
When you have verified your versions, just run the SharePoint Yeoman template as usually.
Then it is time to add the Aurelia stuff. I have put everything on single lines to make it easier to read.
npm install firstname.lastname@example.org --save npm install email@example.com --save npm install firstname.lastname@example.org --save-dev npm install expose-loader --save-dev npm install @email@example.com --save-dev npm install ajv@^6.0.0 --save-dev
It is very important to use the exact versions above. Later versions of the aurelia-webpack-plugin webpack 4 and SPFx is using an earlier version. The latest version of bluebird typings depend on TypeScript version 2.8 or later. SPFx is using 2.4 currently. I also included ajv since npm complained about a peer dependency.
Everything else works in the last post. Happy coding!