MacBook – Which MacBook supports Thunderbolt 3 and has regular USB 3 ports

Thunderbolt and USB are quite different protocols, so you can't just use a cable -- it would need to have active electronics in it to convert between the protocols. And that means it would cost a lot more than a cheap commodity USB hub and so no one would buy it -- they'd just get a hub instead. If you're concerned about the power drain, get a powered USB hub.

Looking at the Traktor Pro 2 Specifications page, doesn't have any requirement that the USB port must be bus powered or host only. In fact, they even state there is an optional Power Supply available:

So, the PS is only required if you can't get the 5V .5A from the bus (host). In this case you have a couple of options

• Use the Power Supply
• Use a powered hub

As for going Thunderbolt to Firewire then to USB, I am a proponent of using the "right tool for the job." Can you do it? Yes. But it's a bodge.¹

Insead, go directly from TB to USB with a [Thunderbolt to USB adapter][2]

Finally, you never did say why your USB connector doesn't work nor which one. In my experience, it could be a very inexpensive fix to repair the connector. This is definitely something you should look into.

¹ Bodge: Verb. 1. To do a poor job or repair. 2. To cobble (something together). E.g."I bodged together that furniture out of driftwood and old egg boxes." From A Dictionary of UK slang.