Here are some thoughts:
1) Never train on an injury. When you’re this acute there isn’t much you can do but rest, ice, anti-inflamatories. If there is an activity, swimming comes to mind in this case, that woudl completely not affect your area of injury, then you could try doing some of that. But I’d ease into it to test the waters, so to speak. Cycling could offer another possible option for shin splints.
2) ARC is something we use often in our coaching work with people who are working on rock/technical climb fitness as well. Yes, count the time the same.
3) Indeed, not all drink mixes are the same. Mixes with a lot of carbs are designed for performance during races, remember at the highest intensity even well trained athletes are burning a lot of carbs. So cyclists in racing scenarios will want to on-board a lot of carbs on a consistent basis. Of course with aid stations and aid-cars, a cyclists never has to worry about running out. You have to carry what you use which make fat adaptation more valuable to you. Remember the saying, train low (carb), race high (carb). Or to put it another way, on your long duration training use only water or a low-calorie drink tab and On the climbs that count, go all in on the carbs.