Are LED panels worth buying?
Generally, their colour is incredibly average. Also, you'd need to spend a lot to get one without enough output to combat daylight.
I've used them as little fillights etc. in the past, but I'm not the biggest fan.
Spend a day in the same conditions as you'd like to shoot at your location. Check out what the sun's doing, where it's going to be at certain times. Often, you don't have the time to do that, so I use the sunseeker app to figure out where the sun will be so that it's perfect for us to shoot in.
Google Earth also has a cool little sun simulator.
As far as on the day - it really depends on the style/mood of shooting You may want to put off that scene to a cloudy day if that's the feel you want, you may want to put it off to a really hot, bright sunny day if that's the feel you want. You may use a bright, sunny day, but diffuse with a large butterfly to soften the sun's shadows just slightly.
I use a large-ish bead-board for reflection, I'm really not a fan of hard silver reflectors. One side is white, the other has Rosco soft silver on it, which is a bit nicer and softer than hard silver, but gives a bit more light than white.
Often, I have unbleached muslin clipped over the soft silver, which is also good for reflecting or diffusing.