The Tiagra (4700) will be fine, it has the same ergonomics as 5800 & 6800 (the hood SKU's are the same), the only major difference is it's 10 speed, the others are 11.

For the sizing, from your height the 56cm sound right, but brands vary, some you need smaller, some bigger. The sale person should be able to guide you through this. Given you have already test ridden a couple, sounds like they are helping with this already.