1. I found a post about an aftermarket trunk net here:
what-did-you-buy-your-ex-this-week-t541 ... l#p6682295
2. I believe that Infiniti did not recommend to tow with the EX. I don't know if they changed their stance with the QX50 refresh, so you might want to check in the owner's manual. That being said, an aftermarket hitch receiver (Curt) is available for purchase and installation. I think there may be one or two forum members here who have towed light loads with their EX.
3. I don't think there are that many common issues on higher mileage EXs. There was one in regards to a small leak at the timing cover seal, but I believe it was remedied with an updated design on newer models.
4. My wife has done most of the snow driving in our EX, and she never felt nervous about driving in the snow. I'd say she actually felt quite confident; and this is with all season tires.
5. If you have the factory roof rails, most universal fit aftermarket crossbars should be able to mount up there without a problem. Just pick the brand you prefer. Some of the members here did not like the OEM crossbars because they are fixed and their mounting distance was short, severely limiting the number of rooftop box models that could be mounted on them. I do not know if this was changed in the new QX50 with it's added length.
And if you don't have the factory roof rails, see this post:
roof-rack-and-cargo-carrier-options-t608785.html