The majority of staff will likely interact with their team who will be positioned near each other and won't need to do frequent cross campus trips. I'm sure they have communication tools like every other office to allow people to get in touch. I worked in a moderately sized four story office space for a year, was involved in dozens of meetings over that time and can still count on one hand the number of times I had to go to the top floor given IT was on the lower levels.No, that's a good question. A ring is probably the worst imaginable plan for moving through the space. You can cut across the middle of the ring if the weather is conducive but even then the journey is complicated and lengthened considerably if either your origin or your destination are not on the ground floor.
A quarter of a miles not that long anyway. I now admin an IT system out of a hospital and will frequently walk 100m to half a KM to get to staff to do on site support. It only takes a few mins. I enjoy the walks and given Apple is putting in fitness centres, trails etc, they are looking to encourage active lifestyles anyway so if staff do need to walk, it's likely not an issue. Apple probably wants people cutting through the inner gardens.
A narrower but longer (in this case circular) building lends itself to things like getting more natural light in too which is desirable.
I don't know the answer, but there's surely travelling happening for Apples existing employees anyway at the main Campus. As far as I'm aware they're in dispersed buildings and locations right now, and the same would apply where some will go between offices while others will likely stay in a single building most of the week. At least the new campus has an option to travel from A to B under cover.