I think this is a beautiful European and Hebrew name. It is both modern (a standalone name) and traditional (as a diminutive of Esther). It means sweet in Basque. It's short and can be easily pronounced in many languages. It is unique and you can hardly find any references to Esti online (as of 2018) - most is of Ezti, Esty, or other variations.
Estivalia… beautiful! Gorgeous word. ^^ Estitxu and Estibalitz are also really beautiful. I also really like it as a nickname for Esther.I heard that it does, indeed, have something to do with “Star” or something akin to that. That little pronunciation thing offered helped a lot, too; I had been saying it “ESS-tee”, which sounds a little too close to “Estee”. I like it.Also, here’s to assuming that “Esty” is just a variant of “Esti” or “Ezti”, and basically is just spelled with a ‘Y’?