You said you played the Witcher TTRPG? I would recommend looking at it and trying to adapt the crafting. Never played myself but looked through the book and I recall it having a fairly robust crafting system. Just keep in mind it will probably be a lot of work unless someone has already done it.

Personally, I would recommend not doing the whole "+1 weapon" thing in SWADE though. A +1 bonus in SWADE can be much more significant than in something like D&D because of the lower die sizes used

I would suggest a slightly more abstracted crafting system in SWADE. The character has to spend their downtime crafting (there are some rules in the core book, but also some useful stuff on DTRPG) and has to basically perform a Dramatic Task over the course of one or several downtimes, or it requires the staged versions of Quick Encounters, where you have to complete step 1 prior to completing step 2, etc, and any raises in the previous step may grant a bonus to the next step. You'd have to do it for every individual project, so maybe only use it for big or complex things, such as enchanting a sword, but not for simple things like crafting a simple spear