Thanks for the advice so far! I landed in Ho Chi Minh yesterday. Traffic and roads actually seem perfectly fine and organized by Asian standards, at least from what I have seen so far around District 1.
I would theoretically like to ride the bike around Vietnam and then into Cambodia (details seem grey as far as how easy it is for a tourist), with most likely a 30-60 day stay in the two countries making buying a bike more attractive in theory compared to renting. I haven't visited any rental/sales shops yet so this is just scratching the surface right now. Will explore the city on foot before I seriously start looking into the bike thing.