Just start with a compression test, dry, then wet, which gives you a baseline.
I keep a sheet of paper in the back of my shop manual with compressions by date, and valve lash by date.
You have an issue with guides not allowing valve to seat sometimes, spring, cam, leakdown won't tell you issues with rotation based compression.
Been doing this what, hobbyist and professional almost 50 years, leakdown is last if the compression testS show an issue you want to pursue.
Only time I ever saw anyone start with leakdown was an air cooled VW guy who worked for me in about 1980. I just let him do it his way.
Generally he would end up doing a compression test anyway.
Worst part is folks who pull ONE plug, test that hole, put it back in, pull the next plug, and so on.
First, the engine does not spin freely enough, and head gasket leaks between cylinders will be much harder to locate.