How do I get a replacement for the nuts and bolts that came with it?

I don’t know, if you never received them, I would perhaps, return it for new on. If you receive them, and somehow they became missing, I would contact Amazon about how to replace them. It is a great cart. I hope you were able to get the parts you need to put it together.

Does this come with 2 springs?

Springs? No there are no springs on the cart. I have never seen springs on any of these types of baskets. What would require springs on it? No, No Springs.

Will it roll up steps?

Yes it will, pull it backwards up the steps using the big wheels

How much weight will it hold?

I have put about 4 gallons in the small part which is equal to 32 pounds. (Water is 8 pounds a gallon). In the big front part I put a 16-pound bag of cat food, a 5-gallon cat litter pail which weighs 35 pounds and about 6 bags of groceries. Not counting the weight of the bags of grociers probably about 10 pounds maybe 15. All the other stuff comes up to 83 pounds ad about say a low estamate of 10 pounds for the five bags of groceries, comes out to around 93 pounds probably closer on 100 pounds.