I am a newbie, so please be gentle with me

I recently bought Asus RT-AC68R router and use OpenVPN on my HTC One smartphone. The combination of the right router and a good Android app like OpenVPN Connect definitely makes it worthwhile to do secure connections.
I have a question. I have been hearing a lot about Android is very prone to malware. Every time I installed some app, free or paid, there is warning about the app could access personal space on my phone. So, can an Android app access personal credential setting (user/password) and the .ovpn file that I imported into the OpenVPN Connect app and steal those information to hack into my LAN network?
I am wondering if using Samsung's KNOX technology on a Samsung's smartphone would improve the security? With KNOX, i will install the OpenVPN in the protected space, while other apps are installed in the non-protected space. I am thinking of switching to Galaxy Note 4, when it comes in Sept this year. it will have KNOX installed.
Much thanks in advance.
Peter