I'm using 19.07.2 for some time now.
In the mean time several packages are updated as can be seen under software-updates. Can i just install them one by one (top to bottom) or should i consider some kind of sorting?
Upgrading via Luci carries the same risks as the process using the command line.
opkg upgrade can result in major problems. It is generally highly discouraged, unless you know what you are doing or if there is specific instruction to do so.