1. Yes, that's one way to go about it. You can clearly do heavier weights than your 5RM on negatives, so you can still increase your load somewhat from there.
2. This is a tough one. You can stick to doing your usual number of sets, or stop an exercise when lowering the weight starts happening faster than it should because you are hardly able to resist it. Naturally, you should also cut back if you notice joint pains, or whenever you feel you are burning out.
3. Your increments are mostly decided by your max weight. The bigger it is, the bigger the increments you can make, and the reverse is also true. Generally, your compounds can easily allow 5kg increments, but isolation exercises won't. As for which one produces more growth, it has been said before that smaller increments are geared more towards strength, and bigger increments for hypertrophy. However, it does not matter the absolute size of the increments, but rather the clear progression of weights. As long as you are lifting heavier weight over time, and you observe a proper diet, you are good to go.
4. As above, it is not the absolute weight of the increments that matter. That said, however, your core exercises most likely should be heavy enough to allow >1kg - such as bench press, deadlift, rows/chins, squats - may be relatively lighter and thus increment with much smaller weight, but you are still good. As long as you are lifting heavier weight over time... you get the idea.
5. Far as I remember, triples are a favorite of powerlifting / strength-training buffs. As the name implies, you do 3 reps, like having a 3RM phase. I am not a powerlifter, and strength-specific training is hardly a field I am interested in, so I can't really say much about it except for what I've told you, which I've only gleaned from other members in this board years ago.
