You can't prevent forced font calculation, anyway that should occur only ones at first startup. On dumb phones (with ahead-of-time compilator as in sony ericsson devices) calculation run 10-20 seconds until operation is finished (c510 is the champ). On s60 takes up to 50s with .sis app and something like 1% per minute with java version so I can only guess that Opera Mini doesn't run near to native code on all devices.
Opera Mini isn't available for BlackBerry phones that run the latest BB10 operating system, like the Q10.
The Opera site is not properly detecting the BlackBerry phone model and is presenting the download links For Opera Mini for BlackBerry OS7 and older.
... over Wi-Fi if your phone has it, that will kill roaming prompt. There is nothing else you can do except disabling roaming messagge, perhaps that can be done via hidden service mode/settings handled by dumbo TouchWiz.