I should let you know that I am not anti-utilitarian, far from it. I'm just providing some devil's advocate arguments which are important to reckon with.

a) In an election of substantial size, the likelihood your vote will make a difference is beyond miniscule. Therefore your time would be better spent elsewhere.

b) and c) I edited my post to add more critiques and changed the order, so I'm not entirely sure what you're referring to. If you're talking about the problem of needing to devote your life to making money and then giving it all to charity, then there are a few counterpoints to your defences. Firstly, it's not great for an ethical theory to say "it's not my fault I don't work, it's the global economy's fault". Alternative approaches like virtue and deontological ethics purport to provide answers as to how to live in this unjust world without being asked to do the impossible. Secondly, a utilitarian will only be able to sit back and enjoy their life once humanity lives in a utopia; until then, they must give up their lives toiling away for the betterment of any who suffer, assuming that the suffer the utilitarian feels from toiling is less than the difference they can make to others' lives, a fact which does not depend on any economic system. Thirdly, Singer's defence of one's own wellbeing as a tool to help spread goodness might be seen more cynically as an excuse for not doing more. Singer is a great philanthropist, but he only gives away around 40% of his wealth, not 90%. He isn't surviving on the bare minimum, which he could achieve by living in the cheapest possible accommodation, eating the cheapest foods, using next to no utilities, moving to a country with the cheapest cost of living while maintaining enough sanity and geographical connection to continue bringing in income. If you pressed him, I expect he would admit that taking care of his family to a decent standard of living comes first.