As for measuring: in my opinion the place to put on ruler depends on the person. The clue is to just be consistent in that type/method of measuring for example if You measure on the top just keep doing it this way and You will be able to monitor Your gains.
Jelqing can be done by beginners as good as by vets, it’s a kind of an ultimate PE exercise for all PE-ers. I wouldn’t recommend any sort of pumps/ADSs/etc. For newbies, but on the other hand if You will use it wisely and get good results, maybe that’s the way for You..
As for supples: take some mineral-vitamin supplementation for overall health. Also, keep Your lifestyle healthy- You won’t regret running, eating vegetables, chicken meat etc. If You are interested in increasing shooting volume search for a “Holy Grail of Cum.” thread. Some of PE-ers got improved EQ and even gains(combined with good routine) from arginine. You’ve got to learn a lot about the physiology, anatomy and PE but on this forum You will get it all.
Keep on train and gain!
P.S. As for routine I recommend Linear Routine; You can learn if You are “less is more” (or not) condition yourself to PE and get some gains.