Hi all, I have a few miscellaneous questions about the freshman first quarter I'm hoping some Sophomores can answer. I am desperately confused

. Feel free to answer just one of them!
1) Is Math 51 very challenging if you have a reasonably solid understanding of linear calculus, but no exposure to multivariable calculus? Does the 50 series fulfill all the requirements that 40 series does?
2) Is the ACE series worth it in either Math 41, 42 or 51? I am a prospective engineer, but I fear the workload may be too intense. Does ACE add homework and exams, or does it simply increase class time?
3) Since Physics 41 is not offered in the Fall, and most mechanics courses depend on the 40 series, what do prospective mechanical / electrical / aerospace engineers take their first quarter freshman year in terms of physics?
4) Is there a formal placement system for physics and math, or will I only discover my qualification for certain courses in the first three weeks after I've tried them?
5) How come online applications to Intro Sems are unavailable as of now even though the application process opened on the 17th of August? Is there another way of applying?
6) In the long run, do Engineers get to declare their major as late as everyone else, or must they decide earlier?
7) How does one approach such courses as SOC 161: The Social Science of Entrepreneurship (SOC 261) that have no posted prerequisites or restrictions? Are Freshmen allowed to enroll in courses such as these?
Thanks if you've made it this far. If your interests or questions are similar to mine, feel free to post away. Hopefully some wise soul will deliver us from confusion.
BONUS question: If Abe Lincoln and George Washington got into a fight, who’d win?