I'm unsure if you will encounter issues with the Plug-In model as it might be setup different to the PS1000/2000 which are universal hence you won't have issues if you run a franky engine as long as the sensors etc are recognised by the ECU. You'll have to contact Haltech directly for that answer.

As for the build gets serious, Haltech you're looking at and the ones I mentioned are powerful standalone ECU with high resolution and advance features, you won't have an issue with 'serious' builds. If they can handle a 4cyl ITB revving to 11,000RPM, they can handle what you're throwing at it =P