How can I efficiently migrate from Cybertill to Shopify for a craft education charity?

[MSW-24]

We are a small craft education charity based in the UK. We also house a craft gallery and shop. We currently use a complicated and outdated platform for our POS, called Cybertill. We've been on it for ages but it is far too complex for the size of our organisation and we want to simplify. We currently use Squarespace for our ecommerce. We are keen to move both over to Shopify so that our stock system (physical shop) syncs with our online shop stock.

Migrating the online shop seems like the easy bit and fairly straight forward. I am finding it a little more difficult to find solutions to replace some functionality from our current till system...

In our shop/gallery we sell the work of our network of artists (over 250 of them), and take a commission. The commission rate can vary slightly. 

Can anyone help me with a couple of things I am struggling to understand? 

Suppliers: the only way I can see to add a supplier is by creating a PO and from there creating a supplier.

1. is this the only way to do it? Is there a way to bulk upload suppliers? i.e. when you are migrating a list of suppliers from an existing system. 
2. is there a way to see a list of suppliers? Like how there is a database for customers? 
3. is there a way to amend the details held for suppliers? On our current system, we record their bank details and use this as a secure record (a database, not for processing payments). 

I have been playing around with Vendor management apps instead - is this the best way to go? 

Thanks!