Personally I found Rome very warm in October - most of the time I was just wearing a t-shirt, though I did need a fleece some evenings and a waterproof one morning. I think Michael's clothing advice is spot on, although you may wish to modify it slightly if you are very affected by heat or cold.

Either a backpack or a smallish roller would be fine; personally i'd go with a backpack on account of having to walk to hotels along busy or cobbled streets. The Leonardo train from FCO to the city centre is pretty good for luggage space and public transport in most European cities is Ok but obviously the smaller your bag the easier things are.