Hypothetically speaking, if someone wants Hashem to bless them with great wealth, would it be irresponsible for them to donate 100% of their earnings to charity? Would they end up poor?
The code says he should give according to the needs of the poor "if his hand is capable." Rema specifies he should not give more than a fifth of his profits. Even some greatest Tzaddikim did not give than a fifth. Becoming rich should not be the motive but rather for the joy of the mitzvah itself. You might be thinking of Micah 3, "Test Me and see if I will not open the windows of heaven" when you bring in the tithes but I think this is a national exhortation and promise, not necessarily individual.
Shulchan Aruch | Yoreh Deah #249
How much should one give and how should one give it? In this regard, there are sixteen sections:
Section 1: The measure of giving, if one's hand is capable, is to give according to the needs of the poor. And if one's hand is not capable, they should give up to a fifth of their possessions, which is a distinguished commandment. And one-tenth is a moderate measure, less than that is considered stinginess. And this fifth is from the profits attained each year.
Rema: A person should not squander more than a fifth, as they may need it for others (Ba'al Ha'Itur citing the Talmud). However, during one's final moments, a person can give as much charity as they wish (based on Rashi, Rosh, Ramban, and Mordechai). And one should not use their own tithe for other commandments, such as candles for the synagogue or other commandments, but rather give it to the poor (Maharil, Laws of Rosh Hashanah).
If he's poor depends on what assets he has so it depends. Having savings to last a year is considered not poor (add source). For individual decisions talk to God and run your idea by decent, reasonable people.
I found in Sefer haMidot giving charity raises your mazal, leads to faith, and brings the rain (#6, 29, and 47). Item 69 however brings that one who shears (גוזז) his possessions is saved from the judgement of Gehenom. This sounds like he gives away all but the skin on his back, but requires more looking into. There's a Sefer haMidot with sources but I don't have it.
There is a concept of hishtadlus. It means that you have to do your due diligence to access that which Hashem wants to give you. The other side is hasgacha, that everything that happens is only because Hashem made it happen. We have to do our hishtadlus. As a person's emunah gets more and more and their trust in hashgacha gets higher and higher, their hishtadlus is less.
One could technically attain a level where they needed no hishtadlus whatsoever - but that would takes level of emunah that takes a whole life to attain. On our level we need to do reasonable hishtadlus.