Well, welcome, first of all!
Runways 34L and 34R are used when there is some strong wind coming from north and this happens often during winter but rarely during summer. The preferential Runway Configuration is as follows: Rwy 25 for TakeOffs and Rwys 16R and 16L for landings (16L national and EU arrivals, 16R for non-Schenghen arrivals). Obviously there is always a little chance of winds from north, but don't trust it so much!
If you will be in FCO during morning, I suggest you to take some pictures at the "Carrots field" (the morning side of Rwy 16R), better if you wake up early and go there during or soon after sunrise (you will get some very nice shots and very interesting wide bodies). After 9 am the heat haze will probably waste your pictures. You can try "Hill" spotting point on Rwy 16L, where planes are some meters higher and the asphalt haze can bother less.
You will need a car for all of those positions
If you have further questions, feel free to ask!