Import data from previous system

Hi, I am a new user to ERPNext system.

We are still using a saas POS for our store operation and currently we need more than POS system.
We would like to use ERPNext system, especially implementing the POS system.
But we are considering to import our old data to ERPNext so we can still have the history from previous system. Old data refers to the sales and sales items.

Is it possible to implement the POS system first to replace our current POS and import the old data later? and if we import sales and sales items data later, will it reduce the current inventory data?

Because if it reduce the current inventory, it would be troublesome to setup the starting inventory data.

or we need to import the old data first then implement the POS system?

or maybe it is better to start all from scratch?

Sorry if my question is unclear. Because English is not my first language.

Would strongly suggest you close books on your old system and migrate balance sheet using Journal Entry Opening. It’s too difficult to migrate invoice related information. Move Items information, customer and assets information only.

Keep old system alive till you need, you can discard it after you have closed 1st year financial year on ERPNext. Or keep it alive for a year more.

Have gone through the nightmare once. And that was an experience for life.