gocr | OCR implementation with Golang | Computer Vision library

Please allow me to ask a rather newbie question. So far, I have been using local tools like imagemagick or GOCR to perform the job, but that is rather old-fashioned, and I am urged to "move to google cloud AI".

I have a (training) data set of various documents (as JPG and PDF) of different kinds, and by certain features (like prevailing color, repetitive layout) I intend to classify them, e.g. as invoice type 1, invoice type 2, not an invoice. In a 2nd step, I would like to OCR certain predefined areas of each document and extract e.g. the address of the company sending the invoice and the date.

1. In a modern platform as a service (pass), I have already set up an UI where I can upload new files. These are then locally stored in a directory with filenames (or in a MongoDB). Meta info like upload timestamp, user, original file name is stored in a DB.
2. The newly uploaded file should should then be submitted to google cloud which should do the classification step, and deliver back the label to be saved in the database.
3. The document pages should be auto-cropped, i.e. black or white margins are removed, most probably with google cloud as well. The parameters of the crop should be persisted in the DB.
4. In case it is e.g. an invoice, OCR should be performed (again by google cloud) for certain regions of the documents, e.g. a bounding box of spanning from the mid of the page to the right margin in the upper 10% of the cropped page. The results of the OCR should be again persisted locally.

I seem to be missing the correct search term to figure out how to do it with google cloud. Is there an google-API (e.g. REST), I can use to upload and which gives me back the results of steps 2 to 4?