Hello there, just a little sharing from my own experience. I started riding after more than 20 years of driving and decided to get a 250 cc (around 21 HP bike). Top speed using GPS is around 120 kph but normally comfortable riding is around 90 kph. Like you, I didn't think I needed the speed and I was mostly riding in small towns and trunk roads. It is until I visited the big cities like JB or KL that I started feeling intimidated. Slow bike in a 6 lane highway especially when you come to intersections on highways can be quite a challenge and sometimes you really need the speed (say a lorry driving at 90-110 kph on a highway). That's when you'll feel torn... overtake it and you have to maintain almost max speed of what your bike can do. Don't overtake it, you stay behind and get smoked to death.

For used bike, depends if you want a twist and go bike (to learn) or you want a full clutched bike. If twist and go, consider scooters (Modenas Elegan 250). If you want a clutched bike, can consider 2nd hand Honda (CB250R) or Yamaha (MT25). If you don't mind some DIY (and some self repair sometimes) but want to ride in style, then you can go for bikes like GPX250 (cafe racer), QJ SRV250 (cruiser), Royal Alloy TG250 (scooter), Italjet Bucaneer 250i (cafe racer) and so on.