For the lime plaster you will need 2 parts sand 1 part lime.
The mix should be "dry" or it will crack. when you lay your layers, do them (build them up) in 2 wet-into-wet passes, meaning

lay first pass and float it with a small float and in about 15min lay another one over - that will be one coat.
as oppose to trying to lay one thick one.

let dry and go to the next layer, if the wall is small (can do the whole layer in one day, you can work the whole thing wet-on-wet (3 doublecoats in 3 days).

search online for Niagara Lime Putty - this one is not good for fresco (has a lot of magnesium) but for lime plaster wall will be just great - little easier to work for conventional plastering. They also have own datasheet with ratios.
http://www.graymont-ut.com/prod_niagara_lime_putty.shtml