Russian Diminutives

I'm writing a story with Russian characters and want to make sure that I'm using proper diminutives for them: I have a Валентин (Valentin) and initially, I thought that Валя (Valya) would be the right short form, but now I'm wondering if Валик (Valik) would be more likely because it can't be so easily confused with Valentina.

I also have an Иннокентий (Innokenty) and have been using Кеша (Kesha) as his diminutive, but am wondering if it's too associated with parrots (and cats?) for people to use that one much. If so, what would be used instead? And just how unusual is Innokenty as a name in Russia? Would you ever meet an Innokenty under the age of thirty these days?

Спасибо!