Is striving to increase income through overtime work, which may affect performing prayers in the mosque, included in "Whoever is preoccupied with the worldly life, Allah will scatter his affairs and place poverty before his eyes," or is it considered seeking sustenance? And what is the ruling on dedicating 5% of one's salary as charity with the intention of increasing income?

Your obligation is to perform prayers in congregation, not necessarily in the mosque. If you do not neglect your duties, and your efforts are directed towards paying off your debts and fulfilling your needs and the needs of those whose maintenance is obligatory upon you, then we hope you will be rewarded for that and not be subject to blame. The only financial obligation upon you is to pay zakat if your wealth reaches the nisab and a year has passed over it. If you voluntarily give charity with what does not harm those you support, then it is a good deed for which you will be rewarded.