There's no way of telling what an update will contain without installing it (unless you are rooted, in which case you could download it then copy it elsewhere and see what it contains, but then official updates on rooted phones are generally a bad idea). Otherwise your best bet is if you can find other people with the same model, same software version, same carrier who have installed the update and ask what changed.
Updates can be anything from just adding a couple of carrier bloatware apps to a complete new OS version. Commonly they are patches, which change just part of the system, rather than complete replacements. Its likely that all of the pre-installed Samsung apps will remain afterwards, but it's possible that they may change (including additions or removals).
If you want a bare-bones installation your best bet is to root and work with custom ROMs. Even then, these come as complete packages, but you have more control in that you can choose which you install and can customise further yourself. But once you go that way you don't have official updates any more, and have to manage things yourself. Note that there is no "generic" android you can install on any device: it always has to be built for the specific hardware, so your starting point always has to be a ROM that was built for the i8160.
I will try to upgrade it to 4.x.
