Hi There,
If there is custom module and theme then its hard to say what is working and what is not. because there is big changes between 1.9 and 2.0.
let me know if you are interested
Best regards
Matli Digital
i have worked on many magento sites and have done their ugradation without any error.
Currently i am working as Linux System Administrator. Having good experience in magento installation and upgradation. You can fully trust on me. Please contact me.