Depends on where you live, I can get good linear lab modules from RS Components in the UK, this is a good example of one big enough to power the board and the outboard units:
I’d hit any of the big online parts supply houses and just search for “linear 5v supply”, as long as it is linear all you need to watch for is how much your going to draw with everything hooked up.
For the USB cable you would have to probably unsolder or clip the wires to the pins on the computer side (to keep it off the data line completely), it’s easy and what I do when I need one.
Just remember it is a one direction cable, the modified connector always goes to the computer.
Where shielding with pass through is concerned use this pic as reference, this is a top notch job done on a DSP-10 by W7LHL:
No wires go directly into the completely sealed box. It has fingerstock on the edges to ensure full electrical contact with the lid ensuring continuous RF shielding.
Those posts are the capacitive passthroughs, how they work is there is a direct connection into the box but the wire is surrounded by a capacitive sleeve that bleeds the RF to ground so you can get signalling and power in and out but the RF noise stays in this case inside the box (it is the DSP unit).
You see similar in pretty much all commercial equipment operating in the microwave reqions.
Nothing works better at giving a as near to perfect shielding as you can get.
You do have to remember though that right next to the RF chip on our boards there is a noise source as well, so if you are really keen on going overboard (like if you are doing radio astronomy or something) as has been discussed on far earlier threads on this site the board has ground traces around the RF section that could be tied into a proper section shield as well. I am still working out how to do this myself in a way that allows maintenance of the cabling too.