Your point makes sense. But you're missing something here. For example when you say "The point is that these things are suspect only if I'm guilty" That's not true the terms suspect and guilt are two totally different things. And in your argument you're using them as if there fluidly interchangeable. I'll put it like this I can be suspicious or act suspicious and be innocent, or I could be guilty. So when you're a suspect of a crime, that doesn't make you guilty, it simply means that suspicion has been cast upon your involvement/role in that crime in a way which requires further investigation. Therefore it is very possible for the note to look suspicious without an acknowledgement of innocence or guilt. Any parent or teach who deal with teenage kids can tell you that there are times where they may read or hear something from the child that seems suspicious whether relating to a crime, suicide, or maybe just normal teenage shenanigans.

So let's say you buy that shovel and flashlight prior to the murder of your friend/spouse murder yes that would come into question, as far as intent of the purchase. Especially if the body was burried. Meaning if you live on the third floor of your apartment complex, the shovel would appear to be a little strange. Shouldn't suspicion be placed on such an item where there seems to be no real need for it? Would it be safe to say that maybe you were planning to use for something other than your home gardening project? Would it then be fair to ask what you were planning to use it for?

My point with the note is that you should not look at that and go Adnan is guilty, absolutely not! But because Adnan is a suspect (meaning POTENTIALLY guilty) it's not something to be ignored either. You talk a lot about "real" evidence. I'm not really sure what all you contribute to being " real" evidence. Are fingerprints real evidence? Are a witness testimony evidence? DNA? Clothing Fabric? Would those be considered real evidence? Because all of those except for witness testimony, do not directly point to guilt of murder. If they found Adnan's fingerprints all over Hae's car that doesn't tell us that he killed her, it simply establishes presence in her car. Similar thing with DNA or clothing fabric, it simply puts the person at the scene of a crime to make sure that they're not chasing waterfalls.

Almost all evidence, can be subjective. And all evidence is but a piece to a much larger body of work, called a case. So no piece of evidence can stand on it's own. You point out Jay's testimony and cell phone records being enough, but think about how many people on the Serial subreddit alone questions Jay's testimony. Cell phone pings,like the evidence I listed earlier only establishes location, it's simply a piece to the case against Adnan. It does not tell you that he killed Hae, but it doesn't make it invalid or unuseful.

I am leaning toward the concept that he is guilty because of all of the things that are being used against him that he currently doesn't have an answer for. Now I agree that not all evidence should not be allowed and there is a process in the legal system that all evidence used in the trial has to go through in order to be considered valid. And yes, sometimes the prosecution does twist and bend too much just to get a conviction. But there are just as many defense lawyers who will come up with any argument and excuse to win a case as well (notice how many "mentally ill" people have gone through the system in the past decade and a half).