how does an average wastelander handle Bloatflies, Molerats and Radroaches?

hey're weak enough that a determined enough wastelander could kill one with their bare hands, but I think it'd rarely get to that point because there's generally lots of debris laying around that you could use to club one to death with. Also all sorts of small arms and ammunition are often widely available through trade or scavenging

Are these pests or legitimate threats to the average homesteader?

I always imagined them to be like coyotes

On their own, they're not a huge threat to anyone but the infirm and the young, but when they start showing up in numbers you ought to look out

What's the cheapest kind of armor one could expect from tiny, uncoordinated settlements?

Durable, ususally pre-war clothes like denim and leather jackets. You could layer some sort of protective gear on top of that, leather is pretty common, or if the necessary tools are available metal can be worked into armor pieces. Although I suppose the cheapest cheapest would be the raider approach, just lashing bits of scrap to your body