Develop portal with Yii2 [PART 1]

We are an Italian Web Agency and we have developed for an Holding an intranet CMS. This portal is too old and too weak so we have to rewrite it step by step. We want start to rewrite 3 modules COMPANIES, USERS, CUSTOMERS Backend and fronted have to be separated in the right way. We want to apply to the backend a theme like Adminlte. COMPANIES -the Holding has more the 3 companies -each companies have some fixed fields and some customizable fields USERS -users have some fixed fields and some customizable fields -each users can see data frome one or more companies -there are different users profile (admin, superadmin, editor, writer) with different permission (the superadmin can see all data from all companies, admin of a company can see only the data and users of the own company, editor could see only inserted data for his company...) -each user has a Profile Area (to change password or data) CUSTOMERS -customers have some fixed fields and some customizable fields -every customer can have different contacts -each customers' contact could be assigned to a different USERS (from DIFFERENT COMPANIES) Ex: RADEX is a new CUSTOMER - Daniel White is the Radex'CEO - Max Black is the Radex'Seller Daniel White is a COMPANY 1 customer - Max Black is a COMPANY 2 customer COMPANY 1 see: Customer RADEX - Reference: Mr. White COMPANY 2 see: Customer RADEX - Reference: Mr. Black - Each Customer have a STORY (DATE - ACTION - USER - NOTE) ES: 20/1/2018 - INSERTED RADEX from Mario Rossi 21/1/2018 - RADEX CALLED from Mario Rossi - NOTE: No Reply / RECALL 22/1/2018 - RADEX Call MArio Rossi - NOTE: contact succed / make order PLUS: -add a Calendar (yii2 have a calendar module) - Each user have own calendar and can add event easily from different site page. -implement users messagges (a message send an internal message and an email to USERS email) After this modules we need to implements others. We think that to use custom fields it is useful to use the same wordpress method. ES: user table with FIXED field usermeta table with CUSTOM field Fixed and Custom fields have to be modified by Backend. (we can add Custom Field) Write back if need more info. Thank you.