What's the best method to handle structure and street lighting with a DCC layout?
If I put in bus wiring for my lighting can it interfere with the DCC signal?
Unless you have stationary decoders that control the structure and street lights, there is no need for connecting these lights to your DCC wiring.
In fact, doing so will add additional power consumption without any of the advantages of command control.
These additional power consumers take away available power for your locomotives, controlled cars and stationary decoders.
Should I use a completely different power source like an old power pack?
That's what many modelers do, a perfectly good way to use such an old device.