The FH scan says that Ace rejected an invitation to be a Shichibukai, which seems accurate to me based on his personality. The earlier release by SukiKim says that he was a Shichibukai. I haven't read any other scans. The two translations also differ quite a bit in tone, especially in that one panel with the three admirals' comments.
I don't think Ace will be kicking the bucket anytime soon, otherwise there would probably be a more detailed flashback.
When I saw the two tsunamis approaching, I realized that most of the recognizable powerhouses on the marines' side are devil fruit users. Mihawk (and possibly Sengoku?) are the notable exceptions.