Aloha @Vince Gethings
That's exciting you'll be coming to Hawaii.
For a good commute (less traffic), you'll have to live East of HAFB. For a duplex, you'll have to live West of HAFB. Most duplexes will be more than 45 minutes away on a typical day. A value-add SFH would definitely open your options as far as being close to work and in a good school.
Good public high schools within your drive-time criteria are Mililani and Moanalua. Value add homes (3 bed) in Mililani will be about $600k and in Moanalua they’ll be about $800k.
Not sure if BP will let me put the actual website, but the best one by far is Oahu RE. It will have more than what you need to make a good decision.
Most duplexes will be in the Ewa Beach or Waianae areas. Most will be 2 beds each side, prices begin around $450k. Not very many are bigger than 2 beds each side. Some duplexes are in/around Honolulu, but will be run closer to $1 mil.
Most multifamily properties 4 units and under are $1.2 mil+. Properties under this amount will be in the Waianae area.
As for cap rates on Oahu, 4-5% is pretty common. 7% is a good buy here.