Make sure the bike is the right size.
Take a look at the tyre clearance at the brakes. Do you have room for the fattest tyres you will need, + fenders if you ride in the rain. On this style of bike, I would look for enough room to fit a 28mm tyre + fenders, even if I chose to ride with narrower tyres.
When your feet are correctly positioned on the pedals, make sure that the front wheel does not hit them when you turn the bars at low speed.
Is there a reason you are chosing a flat bar bike instead of a drop bar one. This style of fitness bikes is essentially a traditional light touring bike (the ones designed for fast day rides not heavily laden touring), fitted with flat bars.