Welcome to the world of headphones! You’ve got a fun first setup, it’ll pair well with lots of different headphones.
Regarding cables, don’t worry too much up front. They are a small(er) contributor to overall sound, and from what I’ve read on the forum, really not worth too much of your money till you get into much higher end gear.
Here’s my personal setup, used with my Asgard 3 and dt880’s:
Interconnect: World’s Best Cables (purchased on Amazon). They are a little more expensive than Amazon basics, but really nice quality (good connectors, high quality cable materials). And they are properly shielded, which if nothing else is nice to know. If you want to save some $$$ you can just go with Amazon basics, they are good quality as well.
Power cables: stock is fine. No concerns. I upgraded to the Pangea AC-14SE on the A3. It looks really great and the cost is reasonable. I don’t hear a sound difference, but it looks great.
USB: Amazon basics are my usual go to. They are well built and reliable. I did switch to the Pangea Audio Premier USB cable, just to experiment with separating power and signal. It’s a little spendy, but fun experiment. I do hear a difference on my desk, but YMMV. Just get one that is short (minimum length for your needs) and well built.
Power Strip: get a reliable one that you believe will protect your investment in the event of a power surge. For a long time I used Tripp Lite ISOBAR8ULTRA Isobar 8. Good quality, no issues with it. Reasonable cost. I’ve recently upgraded to the Furman Power Conditioner (PST-8). A little nicer in terms of filtering and internal wiring, but no sound difference (to my ear). Just get one you trust with your new investment.
Regarding power for your DAC, the Modius runs off usb power. Get a dedicated power brick for it, typically you don’t want to run off pc power. My go to is Anker power bricks. Good quality, won’t damage your device, reasonable cost. A lot of people sware by the old little iphone chargers as being low noise. If you have one kicking around it could be a low cost option. I am currently running the iFi iPower 5V power supply. It’s lower noise and designed for audio products. But most people really don’t see much benefit from this upgrade, the internal power filtering in the DAC is typically pretty good.
All of that said, going back to my first statement, you don’t need to stress cables. Get up and running, enjoy the sound. And over time do some experiments with what you think will improve sound or appearance. Above all, have fun. (And report back to the forum on what works for you 
)