A few quick questions regarding ～ておく and the casual form ～とく
Firstly, when changing from ～ておく to the more casual ～とく I'm assuming the verb is first conjugated to the ～て form then the ～て is dropped and replaced with とく and it can then be conjugated following the godan conjugation pattern as in the examples below.
勉強して → 勉強しておく → 勉強しとく
～とく conjugates as godan such that 勉強しときます and 勉強しときました. In the case of verbs that have a ～で ending do they conjugate as どく？
読んで → 読んでおく → 読んどく
～どく also conjugates as godan such that 読んどきます and 読んどきました
Is my understanding correct here?
Also, are there any nuances that make it outright different from ～つもりです in terms of preparing for something? Is it simply that one of the sentences below feels more natural than the other?