Well, the Obsidian Lite that came out last year does use a Li-Ion battery. This is the one, powered by an 18650:
https://ultrasabers.com/product/new-obsidian-usb-soundboard/So, obviously, you'll need that and a battery. You may want to grab a charger too. For the LED, you'll need this one:
https://ultrasabers.com/product/modular-led-system-mls-unit/You'll want a switch, which one depends on what fits your hilt. And, of course, your blade. Now, that's all stuff you can find from Ultrasabers.
What you'll need if you don't already have it is some wire. For simplicity sake, it's easier to buy different colors so you don't get confused on what goes to what when you have multiple wires sticking out of your hilt. Personally, I like to use 26-gauge aluminum wire. Heat shrink tubing is nice to have for going over the solder connections, but electrical tape will work if you don't have or don't want to buy heat shrink. If you use that, you'll need a heat gun to seal the tubing. And, of course, soldering equipment. The good news is, with a 3.7v battery, you won't need a resistor. Sentinel Yellow uses a red and a green LED, (plus whatever color your flash uses) but the red ones are the only ones that really need a resistor with 3.7v. However, Ultrasabers already puts a resistor on the red LED to create the yellow color, so you should be good to go.