Hookworms are good tires. Not as easy rolling as a true pavement slick but far better than a knobby while still giving you some degree of traction if you get off the pavement or hit some dirt on the road. Definitely keep the knobby tires it came with. Larger size tires are typically easy to remove, easy enough that you don't even need tire levers, so swapping for an afternoon trail ride will be relatively easy.
Another tire to log in the back of your brain is the Schwalbe Big Ben. Similar in what kind of terrain it's designed to be used for as the Hookworm and Schwalbe makes quality tires.
There's also the Schwalbe All Grounder. I'll admit I have no experience with it but it's billed as a mixed use tire, so pavement and trails. The tread design looks well designed in that regard.

Ride the bike for now and swap out parts as you improve your knowledge and skills with a bikes. You may very well want to swap the seat for something a bit more suited to your body, change out the handlebars for ones with a different shape or change the gearing. The more miles you put on, the better idea you'll get of how you want to tweak things to best suit you and your riding habits.

Even though your bike doesn't have the mounting points for a traditional bolt on rear rack, several companies make racks designed to clamp on to such bikes, such as this fairly inexpensive one from Rock Bros. Far as a bike bag, there's a thousand options out there and most of them will do the trick. Pick one with enough space of, if you really want to go cheap, just bungee your backpack to the rack or ziptie a milk crate so you can throw anything you want in it and not have it fall off.