A lot of good advice so far.
I was in the Army, so my lessons learned may not be 100% in line with what's in store for you. The Army combines basic and AIT for the most part.
Anyone who wanted to be infantry, a ranger or SF went to the same basic and AIT together. Most drill sergeants are dickheads. It is their job to be dickheads. With that said, pay attention, follow directions, do your best, and only ask questions pertinent to the training you're doing at the time. Don't be the guy who asks the drill sergeant (drill instructor in your case) about lifting weights while you're in the middle of running sprints and doing push-ups. That didn't go over well at Fort Benning. Stay focused on where you are and what you're doing. When you have downtime, then it's okay to think about the future or other things, but don't get too carried away.
As far as your training between now and 26 March goes, strength, endurance, sprint speed, and jumping explosiveness are great to have. It is difficult to be a decent distance runner, which the Army expected and still be strong and explosive in your lower body, so all you can do is try your best because the Army would not let us pick one and ignore the other. Upper body strength is pretty easy to maintain even with the distance running and ruck marches, provided you have time to eat enough.
Excess fat is terrible. The Army hated fat people. Too much bulk, even if it was muscle, did not do men much good while they were in basic/AIT because the drill sergeants gave us anywhere between 30 seconds and 4 minutes to eat each of our three meals a day. After 8 or 9 weeks, they lightened up a little at chow time. If you have a short time to eat, be sure to pick the most nutrient dense foods. There's no sense in eating bread and cereal first. I wish I would have known more about nutrition before I joined the Army. It would have made a lot of things easier.
Everybody has weaknesses and the drill instructors will find at least a few of everyone's weaknesses, then they will exploit those weaknesses, so don't obsess about training to prepare for everything and don't get discouraged when you discover a weakness you never knew you had courtesy of the drill instructor.
As far as your time in the Marines after boot camp goes, don't think about it too much yet. Focus on the present and take one step at a time. Best of luck to you.