Custom bookshelf advice appreciated

Hi All, hopefully the correct sub for this. I have a new home and would like to hire someone to turn the space in between these beams into custom bookshelves with base cabinets below. My main question is how difficult is this with the unfinished beam edes and the corner beam having a cutout? Would it make sense to just add and run shelves from beam to beam or build in place bookshelves with the edges mounted to the beams? I want these to look as "built in" as possible but would rather have it look correct and not make things overly complicated. Sorry if this is not clear, I am no carpenter.