migrating from 8.7 to 9.1.2 suggestion please.

[peep]

Please provide suggestion
we are migrating from IIS8.7 to 9.1 .what are precautions we have to take before migrating .
I have opened a PMR at first they have recommended to install 9.1.0.1 and after couple of emails they said 9.1.2 has full installation which confused me with actual base binary and fixpack .
I was preassume 9.1.0 is base full install and 9.1.2 is fixpack which goes after installing 9.1.0.Please correct me if I am wrong .

1)I would like to know code migration techinques as well . what did you use to migrat code.

2)After installation did you make changes in odbc.ini file ?
did you make changes in dsodbConfig.cfg ,DSODBConnect/cfg files ?