First people over think when it comes to Kicking. My roundhouse kick is more like MT. I have studied TKD and JKD. I do keep my hands up when I kick. Why don't you try it both ways and see what works for you. To me Kicking is easy. But then again I train a lot on my kicks, Kicks are natural for me.
My first instincts is to kick them somewhere. I don't kick high in combat, but I had a friend who kicked some guy in the head with a high roundhouse and knocked him out, They do work, but I wouldn't do that. But if you front kick someone in the solar plexus,if he bends forward, you could kick him in the head with a mid-line roundhouse. If possible use your shin as a contact point. It will do a lot more damage than your instep.
Roundhouse is the easiest kick besides a front kick,just don't over think it to much. Just pivot on your supporting leg rotate your hips and snap out the kick. But do the kick in 1 motion. Don't just rotate then pause then snap out your kick. I see too many people kick that way, and I see it a mile away.
Like Bruce Lee said use what works for you. If you like your hands up then train with your hands up. Like I said my hands are up like MT fighters and not down to my sides. I know people who leave one hand up and one hand down. Remember everyone punches different and kicks different.........
Saludos de Nuevo Mexico