Stress shifts to the first long vowel if there is one; otherwise the initial syllable.

Umlaut:
Stressed short high vowels become schwa before nonhigh vowels, except if there's an intervening semivowel.
Short /a/, stressed or not, becomes schwa before a voiceless consonant followed by a high vowel.
Short /e/, stressed or not, becomes /i/ before a palatal or velar consonant, excluding /w/, followed by one of /e i u/.

Short high vowels are lost from the second syllable of words longer than disyllables, if the first consonant is a plosive or /s/ and the second consonant is a voiceless plosive. The clusters then become geminates - except in the case of /s/, which > ɹ.

z > ɹ
V1ɹV2 > V1:ɹ if V1 is stressed and both vowels are short; otherwise there's hiatus.