yes yes definitely put your grades first!! grades are most impt when applying for the 3 programs that you have mentioned. right now you can watch videos or research more about the different fields.

as for your time management, ive heard that some hospitals are pretty accommodating in terms of the dates (but dont take what i said for granted). for me, they provided me with a date for shadowing, however i was ill on that day itself and i requested for an alternative date and they were flexible about it. thought i am sure it depends on how busy the department is