No. Takes several weeks without proper training/nutrition to lose muscle mass. I was ill for 6-7 weeks this year and after a week back in the gym, I was back to where I was.
Being sore isn't indicative of a good workout. As long as you're growing consistently, it doesn't matter if you're sore or not. That just sometimes happens if you do something your body isn't used...
This, but if you really want to, find out your daily caloric needs and eat 300-500 over that. 1 pound per bodyweight is a safe bet and fill the rest with carbs and fats. Doesn't really matter what...
I like to rotate the focus between chest workouts. One day I'll do 3 exercises for upper chest and 2 for lower, then reverse it the next time I do chest. As for exercises? Incline press is good and...
Workout sets means the weight and reps you want to do to challenge your muscles into growth. So, benching 245 is your workout set. Warming up like you described is great.