Is it possible to connect users with company's branches? while sign in into ERP, They shall have only working branch related data. Giving option in dropdown list to user, there are several man made error without proper dimension or location.

No, separate companies and then import the data on a regular basis (this could be automated) to main company is what I would do.

Yes, same tax entity and yes, different company (dba). Let me explain...
Tax entity is a sole prop.  As a sole prop, the tax entity is the sole prop owner.  But different dba "companies" under the same sole prop have different books, but they need to "roll up". COA is segmented to support this.  Invoice needs to show "dba" name, not business entity name.

Then kvvaradha´s post #4 & #6 above is the info you need or go to https://frontaccounting.com/punbb/viewforum.php?id=16 Jobs wanted forum to hire a developer, but its not a major mod.

OK, now how do I get the location name and address to print out on the sales orders and invoices?

Is this the same tax entity? Or a different company?

Most invoices need to have the address of the head/registered office on them, they don't usually have the store location address; look at a receipt from a chain store - Walmart, etc.

from sales invoice you can get order no from order_. use that and get the sales_order table connected and get the location and connect it with locations table to get it.

But i guess, there it was already collectetd in the sales invoice and sales order pdf templates. kindly check that clearly before making it depth coding.

Set up a training company to try it first and get to know how it works and links together, do some dummy transactions that reflect your actual business; read the wiki and any relevant forum posts

There are no restrictions on the number of locations or dimensions