You really only need ONE flash for almost all situations outside. Unless there's a specific look (or effect) I'm going after, I only use a single flash when outside. Indoor studio is a whole other discussion.

With flash photos outside during the day, keep in mind, you have two light sources. The sun and your flash. I don't even try to overpower the big ball of fire in the sky, so I treat that as my main light.

Then using a flash as fill light only, you can prop it up on something like a rock or park bench, have a friend (assistant) hold it for you and even strap the thing to a tree. Or, spend $10-$20 for a light stand and clamp which will also let you attach a $10 umbrella and now you're shooting like a pro.

As far as color, I went to my local camera store (yay for helping the local guy) and picked up a pack of colored gels for a few bucks. A rubber band around the flash head with one of these will make the light balanced to whatever your main light happens to be.

This means adding a blue filter to match the look of cloudy days, or an orange filter to match the golden hour (setting sun).

If you don't gel the flash then your end result will be a high noon, daylight balanced, blast of light on your subject with the aforementioned color of the ambient scene around them. Unless you're going for that effect, the gel will help keep the colors matched.

Lastly, I personally hate the look of flash on a subject. I always try to make the flash "compliment" the ambient light and be as subtle as possible. So, if using auto TTL flash modes, I use negative exposure compensation of at least 1 stop either on the flash unit, or some cameras let you adjust flash exposure compensation directly in camera.

If using manual flash modes either use the power adjustment on the flash (i.e. 1/2, 1/4 power settings), physically move the flash closer or farther away from the subject, or modify the flash output with things like an umbrella or soft box.

P.S. I only use the pop-up flash as a trigger for the main if no wireless trigger is available, never as a source unto itself. And, I have only used flash for landscapes if I need to light the foreground immediately in front of the camera because it's in shadow. Then it's back to when I mentioned negative exposure compensation for TTL or manual power settings.