Can I drive the strip with the Electron's vUSB since (I think) it's 5v?
Yes, but I would limit that to 1A worth of neopixels (1A/0.06A = about 16 pixels full white). If you want more pixels, it's recommended to tie the GND's together and power the strip independently from the Electron. It's also recommended to use a 5V level shifter on the 3.3V output of the Electron, but you can get away without them. YMMV (Your Mileage May Vary). See the Neopixel library headers for info on parts.
I assume I'll need a 1000 uF 6.3 cap parallel with the vUSB and Gnd?
Recommended, yes.
Will need a series resistor between a digitial pin and the DIN of the strip? Like 330ohms +?
Recommended, yes. 220 or 100 can work well too. The trick is not to round off the square wave too much at the neopixel DIN with respect to GND, but enough that you don't get nasty overshoot voltages.
Will the existing libraries work with the Electron? I read on an old topic that the libraries only support Photon & Core
Yep! Supports Core, Photon, P1, Electron, RedBear Duo.
Lastly, the strip uses 5050 LEDs ... is that like the WS2812b?
Most likely, especially if you bought them from Adafruit.com.
EDIT: