What you said is completely true.
However, studying subject X at level along with Subjects W, Y and Z is harder than just studying whatever you are best at at university.
No, but you would likely handle Biology or Geography easily.
What makes Chemistry and Pysics A Levels hard is the maths and calculations required, not the actual scientific understanding behind the subjects. Also at Uni, you are allowed to use Excel and other programs to do all of your calculations for you on coursework, whereas in A level Chem, we had to do calculations for our lab work under exam conditions, and on a few occasions our teacher actually broke the rules and let us take them home to spend the rest of the day working on them because he thought that it was ridiculous to expect us to be ables to manage to do them in 30 minutes.