How to Tell if Tobacco is the Right Humidity?

I am a total novice so take this for what its worth. I have done some research on this very subject and this is what I came up with. It should NOT be crunchy when pressed between the fingers, also you do not want it too wet as it wont stay lit in the bowl. So what I do is if it feels pretty moist out of the can I let it sit on a cutting board any where between 15 to 30 minutes prior to packing a bowl, I roll the tobacco between my fingers every 5 minutes or so and judge the moisture content until I think it feels just right. Scientific? Nope. Totally subjective? Yup! You will get the hang of it, and you will certainly know when its too dry.
Don't use an apple or any fruit to rehydrate dry tobacco, you are asking for mold. Just put the tin with the lid off in a plastic Tupperware container, wet a paper towel and ring it out so that its still wet but not dripping. Place the wadded up wet paper towel in the Tupperware next to the tin of tobacco, put the lid on the Tupperware and leave it overnight. In the morning you will have perfectly hydrated tobacco.

There are no rules, and what works for one person doesn't work for another...
This is something that just takes trial and error. And, there is no one clear cut "humidity" for all tobaccos. I know this will sound frustrating, but you just have to try different things, and make a note for that blend to yourself.
I like my straight Virginias and VaPers crunchy, because to me the added steam makes it bite and hides the flavors. To me the flavors that I want out of those comes from very dry tobaccos smoked very very very slowly.
Aromatics, especially the topped ones, I like moist, because there just isn't going to be much flavor there anyways.

Latakias, I am still learning. I don't smoke these often.
But, back to Virginias, even within this genre, I like some to be a tad moist, as in a ribbon cut or some broken flakes. But, on the lighter flakes, I like them to crumble easily. Darker flakes, somewhere in between.
This is something that will just have to come with experience for you. Try, experiment, and make notes for yourself. This is the beauty of the pipe. You can alter the flavor in so many varieties of ways. Dryness, the pipe, cadence, frame of mind, all of this will make each smoke different for you. You can either develop an appreciation of these nuances, or focus on getting a consistent flavor. But, frankly, I think that striving for consistent flavor is boring. Or, at least it would be for me.
Enjoy your exploration, and welcome to the forum.

If tobacco looks too dry, try a small bowl first. Often, dry tobacco smokes evenly and with full flavor. The idea that

it should be springy with moisture is often just not true. Sailors of old, among others, kept their tobacco in cloth

bags for months, and it smoked fine. Yes, they had plug and rope, but I think loose tobacco was still standard.

More importantly, and I'm surprised no one addressed this yet, is not to let it dry out in the first place.

After you purchase the tobacco place it in a Mason jar. After all this time I've never had the need to rehydrate tobacco.

I would also suggest getting the 8oz. jars. That is the size I normally use for opened tins as there is a smaller amount of air. You can fit in quite a lot by simply pressing down the tobacco with the bottom of a small glass. The less air the better if you plan to store it for any length of time. Either way, Mason jars are the best way to go for storing tobacco.

I put my tobacco in 4 and 8 oz jars for long term storage. But I still have a lot of open tins and pouches that I'm currently smoking. I keep these working tins and pouches in kitchen canisters that seem to seal up pretty well. The canisters seem to have been designed specifically for 50 gram tins.

When it feels right. That's my experience after fifty years of pipes. It's a learning experience. Some blends are better very dry, others must have a bit more moisture. This is one of the reasons I stick to tried and true blends that I've become accustom to and know the idiosyncrasies of. Personal taste also enters into the equation.
My rule of thumb is that I like my British a bit on the moist side. Other blends I treat as individual and it usually takes a tin to find the right level.

I'm not sure that other than tobacco that is excessively dry or wet, correct moisture is more than a personal preference. Blenders seem to have their preferences for how they issue tobacco. If you rub your thumb and index fingers together with GL Pease tobacco in-between them, you will find moisture that is noticeable, and although to me this is a little too wet, I'm not going to dispute his findings for how the tobacco smokes best.
Other blenders seem to release tobacco very wet, Esoterica and Sam Gawith, for instance. It's as if they want to make money off water and the tobacco. But as I am not privy to their reasoning, I've stopped disparaging them for the practice. Right now I think that their production process ends in wet tobacco and they choose to ship it out wet because they don't want to take the time to dry it down. Who knows?
Some guys insist that their tobacco be very dry and resort to air-drying or high-intensity lamps. John Patton says that all of his tobacco are to be smoked very dry, and goes further to stipulate that they smoke best in cobs. Again, all of this seems to be personal preference.