1. I think yes you can use deployment user as admin user. In theory, deployment user is basically more powerful like sysdba who can perform all the task without any privilege issue and once the job is done it should be deleted.
On the other hand admin user is an optional user provided to the Pega 7 Platform that is preferentially used by certain features that require creating, modifying, or dropping database schema objects; for example, System Management facilities and certain decisioning operations. This is for better control of the applicaiton.
2. "Basic read and write access to data and rules tables including rules resolution" means Connect and Resource role.
Only correction from Rajeev's comment about is that the base user needs to have create session and insert/update/delete/execute on the objects within the data and rules schemas. You don't specify what database you are using and the guide you attached is the platform support guide and not an install guide. If you are using an Oracle database, for example, the base user could be the data schema user. As part of the installation/upgrade the data schema user would have been granted all of the privileges it needs on the objects within the rules schema and of course he can already access anything that he owns.