the IB classes would be for the certificate because I have no interest in the entire diploma
Ask them. It probably doesn’t matter, so long as you’re taking the most rigorous classes.
If your school offers the diploma, then that is likely the most rigorous option, only take a mix if you love a class enough to take HL. HL in most classes is more rigorous than AP.
If you can take the full IB program and get an IB diploma do it. Otherwise the IB courses are not viewed mire favorably than AP classes.
IB Diploma can get you many college credits at some schools. For example, at SUNY Binghamton:
"Students in the International Baccalaureate Diploma Program may receive up to 32 credits. To receive the full 32 credits, the following conditions must be met:
The IB Diploma must be completed with a score of 30 or more points; and
The student must complete at least three Higher Level exams with a score of 5 or higher.
Diploma holders who meet these conditions receive credit for their individual exam scores plus additional liberal arts elective credit to total 32 credits."