Process Approval Hierarchy

Is it Possible to have such an a process approval hierarchy to manage company internal purchases of materials. where by I can now define users and involve them in the approval process.

You need to configure workflows for approvals:

Yes, I was doing that earlier but got a little confused, when choosing document type,should I select Item Attribute, Item or Group Item.
I was setting up workflows with Group Item and it only allows two workflows as active,the rest are deactivated automatically,made me wonder if theres something Im doing wrong.
I also noticed most of the processes fall under the same workflow with little to no variations. So what would be the best method to define such workflows.
Please guide, thank you.

For internal purchases, the document you are looking at is material request. Since material request/requisition is where the process will play out before a Purchase Order being raised.

Refer these to understand how the buying cycle is carried out in ERPNext. It will provide more context on setting up the workflow: