I can't offer any direct help with translation, but can suggest that "handwritten notes" suggests a difficulty that my wife has encountered in genealogical research, with handwritten records.
Variations in handwritten script require an "extra translation" on top of the conversion of the language. You might find translators more willing to work with the texts you have if you are able to type them as clear "printable" text. If would be assumed that you'd need to use a Cyrillic font(?), but the "characters" you need are generally available in recent word processors, and a "language" can be selected to simplify typing. Our experience (with German/Austrian records) suggests that you'll run into lots of "ambiguous" characters, but even partial transcriptions may be helpful. If there are significant ambiguities, the translator should obviously be provided with both your "typed" version and a scanned image of the original for each piece.
Having "digital text," even if only fragments, might allow limited "machine translation" (e.g. Google translator?) that would be sufficient for you to guess at subject matter to select which things to work first, although results with this kind of conversion are extremely "variable."
The author's avocation as a Russian Orthodox priest suggests that the things he wrote about might be of interest there. It would be a place to look for someone "interested enough" to look at the translation task, initially at least for a few pieces. If you have something of value/interest to their church, it shouldn't be necessary that you still have a church association there.
If an accessible school (probably a university) teaches languages, that would be a good place to look for someone to help you. Depending on the complexity of the work, an instructor might be interested or might be willing to assign "pieces as homework" for students.
If you are considering publication as a book collection, you eventually will probably need a single translator - to be credited as translator in the publication - in order to put things in consistent form, but that can be determined when you have enough done to approach a publisher.
These observations are based on "some experience with book publishing" but virtually "no knowledge" of languages, but may get the thread started so you'll see better advice from others(?).