In my opinion, building your own /e/OS-ROM is not as easy as it is shown here again and again by connoisseurs of matrery. The instructions are meaningful, but whoever lacks basic knowledge about Docker container platform will have to fight for a long time until the result is right.
@shadowfax, your first experiences with flashing a custom ROM were catastrophic - and everyone knows it: Once bitten, twice shy. But you still want to try it again - otherwise you wouldn’t be asking for help here, right? But when flashing, there’s always the risk that you can turn your Galaxy A5 into a paperweight that doesn’t turn on or boot.
My experience with Samsung Phone is the same as @ Anonyme. Under Windows with Samsung Odin, flashing TWRP is very easy - and flashing /e/ OS with TWRP is just as easy.
My very first step would be to make a full backup of all the partitions, i.e. /Modem /Boot /System /Data and especially important /EFS. Saving to an external microSD card is highly recommended. This would save your current configuration with StockROM Android 8 Oreo.
Another question: Which ISP carrier in which country do you operate your mobile phone? If anonymity is important to you, please don’t answer here.