Go bigger. Get a cage online maybe as most sold in pet shops are barely large enough for a dwarf never mind a syrian. Same with the wheel, you need solid - no rungs and big enough to run without arching its back. Don't get a cage with tubes. Syrians can grow to the size of a small Guinea Pig and have form for getting stuck.
I have that same Duna cage that was linked upthread. It is perfect for a single Russian dwarf or 2 Roborovski dwarves but I wouldn't put a Syrian in it. The wheel I just threw away as it wasn't even big enough for my russian dwarf as a baby. Took out the top platform as it left no room for toys and meant she could reach the top and swing upside down. As someone else said, the easiest thing to do is make a cage from a storage tub and mesh.
Steer away from fluffy bedding as they can get tangled in it or ingest it. Carefresh is a good bet but I wouldn't get the Eco version as it smells like its already been peed on.
They do bite. When they are babies most hamsters bite. The only breed I've had that don't are Chinese hamsters. They are painfully shy though and take a long time to lose their fear of you. Most of the others bite at least to start with which is why I won't have Syrians, as when they bite you, you bloody know about it. At least with a dwarf they don't normally manage to draw blood.
An exercise ball is a good thing to have too, for when you clean them out.
Wooden toys are best as they will chew them and keep their teeth short. Otherwise they overgrow and you pay a fortune to have them cut every month at the vets.
Go for the one that comes up to you. Look at how they interact with the saleperson. If one comes running up to their hand to investigate, that is probably going to be quite friendly. Most bite out of fear so the more curious the better. Look for soft, clean, shiny fur and clear, bright eyes. Hamsters are clean animals by nature, if they aren't cleaning themselves fully there is a reason why. Check out cagemates. If any look ill, try somewhere else.
Pick a food that doesn't have too much corn and wheat in it. Harry Hamster is a good mix. Some own brand ones are basically full of hamster junk food. I suggest getting some dried mealworms to mix in for protein and feeding a small amount of fresh food a couple times a week.
They tend to like cheddar cheese, hard boiled egg white, small amount of cooked chicken (not fried and not much, it makes them hyper) and most veg. No onions or garlic and very limited citrus as it gives them the shits. The only acidic fruit I give them is a small piece of apple. I avoid oranges and only give dried banana as it sticks in pouches. Mine loves broccoli, runner beans, spinach, cabbage and celery. If you give them grapes, only seedless. A small piece of unbuttered toast or a bit of cream cracker once in a while will be enjoyed too.
Can't think of anything else useful atm hope some of that will be of help.