See
https://www.genze.com/accessories/ The bikes should be mechanically fine though you could always pay a local bike shop to assemble the bike and check the brakes and gears work, it's the battery you need to think about, particularly on older and higher mileage models, or if you want to ride further than 15 miles - but at $500 including shipping you can afford to get a spare battery at $390 including shipping - there are 2 models of battery so you should check with Genze on when a particular bike you are interested in buying was made, if it was made before June 2017 you need the 1st gen battery, if it was made after June 2017 you need the 2nd gen battery.
If you intend to ride in the wet I'd consider getting fenders, if you're thinking you would ride on dry pavement you probably don't need them, but if you want to carry anything I suggest you get the rack and a bungee cord or net and a basket. Buy a u-lock to secure the bike.
Post your impressions here, I'd be interested to read what you think of the bike.