Hi Beth,
In general, I think epoxy resins are okay smell-wise to work in an apartment. In my opinion, the smell isn’t any more noticeable than fingernail polish. DO NOT use a polyester resin. That smell is awful!
As for your second layer, yes, the second layer will adhere to the first layer. If you pour the second layer while the first layer is semi solid (not fully cured), the pour line will be less noticeable.