To what extent does dedicating one's prayers to an increase in provision and blessings contradict the Hadith: "By Allah, none of you truly believes until he loves for his brother what he loves for himself"? And is the supplication attributed to Ibn 'Umar authentic?

There is no contradiction between a Muslim limiting supplications to themselves and their love for good for their brethren. This is because supplicating for oneself and loving good for oneself does not negate loving good for others. It is preferable to supplicate for oneself first, then for others, following the example of prophets like Ibrahim and Noah, peace be upon them. There is no harm in limiting supplications to oneself, as was mentioned in the teachings of the Prophet, peace and blessings be upon him.