(1) Keep the electoral college because it has worked and was part of the original agreement between the colonies so that individual states of lower populations would not be at a greater disadvantage to higher population states for the presidential election
In the original agreement, only the white males over 21 were allowed to vote. White women, Africans and Indians outnumbered White males with property (who wrote the Constitution and were meant by "We, the People." The population of "small states" refers to the number of White males. In slave states, there were fewer of them; so, the electoral college protected their rights.
However, nowadays, "we" are all Americans (with a preemptive fuck you to those who disagree). So, the system should reflect the current situation, not that of 1788.
Your number one is related to numbers 2 and 3. I'm not sure about lowering the voting age to 16, but I remember when 18 year-olds could be drafted but couldn't vote or buy beer. I'm not sure about 16, but I don't see it as a disadvantage to any particular party. Consequently, I wouldn't even consider raising the voting age.
I'm not in favor of "illegal" aliens being allowed to vote. I don't consider any human being "illegal," anyway. But, I think there are people in the military now who are not "legal" residents. There was a report about a Marine who was deported. Anyway, I think anyone who fights for the country should be able to vote. Other than that, I think only citizens should vote. Well, I think all citizens should be required to register, and I think it should be illegal to take away the right of any citizen to vote.