1. You can use org-roam-node-find which (maybe depending on your default completion framework, I use doom emacs btw. so some things are preset) let you type substrings of the actual title of the node to find it.
2. This is a bit complicated, because there is no built-in way for having distinct buckets in Org-roam. But you can set directory-local variables in .dir-locals.el to achieve this.

For example, put this inside the file /home/username/work/.dir-locals.el:

;; -*- mode: emacs-lisp; -*-

((nil . ((org-roam-directory . "/home/username/work")
         (org-roam-db-location . "/home/username/work/org-roam.db"))))

Whenever Emacs opens a file inside the work directory, it will load and apply any variables in this file. Therefore you first must open a file inside the folder to access this files; open a file outside the directory to access the default ones.

Welcome to org-roam!

For opening a file, you can use M-x org-roam-node-find. You can then either create a new node or visit an existing one.

The manual has some info about having multiple directories. It's not super smooth, but it does work: https://www.orgroam.com/manual.html#How-do-I-have-more-than-one-Org_002droam-directory_003f