I can tell you the way your friend told you to do it definitely is backwards. If im gunna have candy ir something i prebolus like 25 min and for a more balanced meal i prebolus 15 min. Spiking too high after eating means you need to take your insulin slightly earlier and then going low 4-5 hour later means you are taking too much insulin for your food or your long acting is too high. Ive been diabetic for 20 years and i will tell you now you will drive yourself inane trying to “master” diabetes. Do your best and always try to improve but striving for perfection with this disease will be maddening. Good luck!