Syrians are a solitary species,so as for living alone it is mandatory once they're old enough to be weaned from a litter.
As for food,start with your high quality base diet(Harry/Hazel Hamster,for example,or a combination of foods using Higgins Sunburst and either Carefresh hamster food or Mazuri rat and mouse lab blocks).Then,you can figure out any safe foods that aren't already in the diet.In the case of Higgins and Carefresh you'll need to add animal protein regardless just to make it completely suitable,ideally Pure Bites freeze dried chicken or another product of the same quality(meaning pure chicken with no additives).
In terms of treats,do stick to high quality and beneficial ones only.I would skip out entirely on Milk Bones and stick to brands that do not have unsafe or questionable ingredients(as those do,including preservatives known to cause cancer and unspecified biproducts).It doesn't have to be expensive though,as Dollar General sell a box of small breed dog biscuits(make sure they're the ones with no unsafe ingredients,as not all of the flavors are safe).Those are very cheap and considerably higher quality than Milk Bones!Another option you should be able to get which is a bit pricier would be certain flavors of the Wet Noses dog biscuits.I'm not sure if you can get them anywhere but Petco,though they're very good biscuits which luckily do come in smaller $2 boxes.I've got the peanut butter & molasses flavor at the moment,and while the box is very tiny it could last a long time with hamsters due to how big the biscuits are(one biscuit would be four servings for a Syrian if you break it up,and the box comes with around 4-6 biscuits I think).The Dollar General ones are just as appreciated though if you'd rather not spend much on them
Gerber baby puffs,depending on flavor yet again,are also very popular!Some flavors aren't safe,but the good side of them is that they're fairly low in sugar as long as you don't feed a ridiculous amount(60 pieces or more,and even that in the organic apple flavor is just 1 gram of sugar).
Higgins Sunburst veggie stix are one of the less popular(but still eaten)treats that I've used.They're cheap if you get them from certain sources such as Petsupermarket or possibly Drs Foster and Smith,and unlike similar treats those are at least healthier and less sugary with no added dyes or flavors.
Going with the crunchy treat theme,Vitakraft AnimaLovens Garden Patch biscuits can be popular as well.They're not the healthiest treat out there but they're far from the worst,and while they do have added sugar there are no unsafe preservatives.They're a treat you could easily skip out on,but if you really wanted to try them it would be fine!
Tiny Friends Farms Gerty guinea pig biscuits(forget the exact name!)are also popular.Some of the Tiny Friends Farms line is unsafe,but these are fine and are definitely a favorite.
Whimzees dog chews are kind of an obvious one.They're available in bulk at a great price with some variety pack options depending on where you go and if there are sales,and they're much healthier than a lot of other storebought treats.These are definitely better than Greenies,and would provide a better surface for teeth wearing as they're much more stiff(Greenies contain gelatin,which makes them flexible and not as good for teeth wearing).