2. Comfort - if it isn't comfortable any other factors are irrelevant. - Grip on wet ground and dry/damp rock. - No wateproof membrane.
3. My Roclite 295's are probably the best I have had so far. Also quite durable. I have one pair about 4 years old that are literally falling to pieces and a "replacement" pair that are about a year old.
I usually plan in advance where I am going to stop. However, most of my backpacking is done in Wales/Peak and since I have been going there for around 50yrs, I am familiar with most of the suitable spots I find it's actually enjoyable to stop early and spend some time chilling out and exploring around my camp site. It's also worth making a note of suitable camping spots on day walks, or your backpacking trips for future reference.