Just be sure to fulfill the basic requirements of LOR/LOE, which are intended to be an evaluation of you in an academic setting first before additional letters from PI and surgical residents. Each medical school has specific requirements which typically fall into ONE of the following categories:
A) 2 professors/instructors you have taken science classes with and 1 non-science professors/instructors you have taken a class with.
OR
B) 2 science and 1 non-science faculty
OR
C) Prehealth Committee letter
Below are 2 versions of the same AAMC guidelines to letter writers which I urge all applicants to give to their recommenders/evaluators when you request the letter