For the novice/intermediate, this is going to take way too much time and effort to meet the requirements you have asked with an Arduino Uno (if it is even possible).
May I suggest a Raspberry Pi instead.
The Raspberry Pi (depending on the model) has multiple video outputs:
- Composite video
- LCD display
Each of these video outputs require very little effort to get going.
Adding WiFi capability requires just a USB WiFi dongle (and possibly downloading a driver) a bit of set-up and that about it. The RPi 3 (Model B) has on-board WiFi so you won't need the dongle.
What you want is very similar to a digital photo frame, so I would search for people who have already done that using google. I imagine that there would be plenty of free code/software out there on the internet.
All of this is a lot easier on the Raspberry Pi compared to using the Arduino.
pcDuino is another hardware platform much like the Raspberry Pi that would meet your requirements. The pcDuino is less popular than the Raspberry Pi and so there may be less open source code out there in cyberspace - but it would still be worth a try.