If you are familiar with the Weatherby Vanguards, then you should be familiar with the Howa 1500s because the Vanguards are not true Mark V actions, but rather Howa 1500 actions. As such, you can rest assured that they are good quality rifles.
As for the triggers, yes, they are adjustable.
Do they should 1MOA or better? Well, that really all depends on a lot of factors. Maybe the gun will should 1MOA with one brand of ammo, but smaller, or larger groups, with other ammo. Let's just say that, generally speaking, Howa's accuracy is better than average.
Zachary