Is there a command to list the files/folders saved in rootfs? I am at 38MB free despite having removed almost everything. It's really annoying that I have no control over what hogs my rootfs.

You can use the StorageUsage app to list packages and their disk usage - it flags those on rootfs in red. There's also some command-line scripts I've posted here which you can use to list all the packages installed in rootfs and how much space they use (it's a bit more accurate than StorageUsage as it takes account of the optified python setup).

Is uninstalling python neccesary for updating python enviroment, or only for update to do optyfing? If the first I may suffer from old version of python (I don't know if previous owner did it, and yes it's second-hand), If the latter it may be easier to use pkgscan.sh script (a script which optifies selected packages file-by-file, which is more likely to not break packages than optyfing folder at once, because folder symlinks make problem with ".." usage) since I have many python-based programs (and i would have to reinstall all them once uninstalling main python package which all properly formed python apps packages has as a dependency).

Is a problem - the need to have free space on rootfs to apply OTA update - a result of non-optyfied apt-cache (or other non optified apt related resources), or some inability of OTA mechanism itself? If the latter, has CSSU same problems as nokia SSU? Anyway without optyfing apt-cache nobody could have all repos from shiny gronmayer site together enabled (as it would seem use 512 mb or more on rootfs while rootfs itself is a bit less than 256MB - entirelly impossible). So generally optifing apt-cache is a good idea.

We (developers, users) have to optify since nokia put busybox inside usr, so we can't make whole /usr an another partition, as this would brick our device as boot process need to have busybox on rootfs. So even having linux ability "partition can be any directory in filesystem", we can't just use it because some files which are supposed to be at usr shouldn't be even there (as /usr has an idea to contain optional things) but they are (busybox is definately not optional since it is needed in boot proces on rootfs, and idea of /usr is broken by that). Nokia definately should make busybox out of /usr - even /boot is resonable - and make non-boot-applications have this accessible through a symlink in usr (if it is default place for busybox generally in linux). Yes that has a flaw that would make boot process even less portable, but then we even wouldn't have to optify, because /usr however beeing less optional than /opt could be made another partition, so devs - including nokia ones - wouldn't have to bother to optify since both /opt and /usr would lay out of rootfs. Nokia can perhaps reason this by the fact /usr/lib would be out of rootfs and theoretically this can cause slowdowns. Even with those slowdowns many users and devs (but perhaps not all) would prefer to not bother with optyfing - as it's one of most annoying attribute of the device (Nokians should understand this that almost all others attributtes of the device is shiny even if not perfectly ideal).