I want to replace my optical drive with extra USB ports

Not a great idea since it’s almost impossible w/o modifying outer case to solder an additional USB Hub. And USB-C is not an option w/o an external controller, which requires either PCIe lanes or something else that uses PCIe lanes (like Thunderbolt). My suggestion, get an optibay and install an HDD instead of optical drive. You can use that HDD to store some junk or files that don’t need high speeds. That can help your SSD to live a bit longer (I know, you said that storage expancion isn’t what you want rn, but it’s the safest way to do something right now).

Also soldering an USB Hub will definetely kill something on your MoBo since there will be problems with either not getting enough current, or screwing up those tiny electrical paths on PCB. So there’s that…