Should I categorize my initial investment in the company as Owners Initial Investment , or Owners Investment ? Should I categorize as partners loan to company ?

Accounting entries must begin with entity type, you seem to be mixing up these 3 entity types:

- Owners = Sole Proprietor

- Partners = LLC/Partnership

- Shareholders = Corporation

Regardless of which of the above you are, you must choose to file taxes as one of these:

- Sole Proprietor

- Partnership

- S Corporation

- C Corporation

This defines how accounting entries must be done. For example, many LLC's file taxes as an S-Corp.

In that case accounting must follow rules for S-Corp, then owners are Shareholders and Employees.

Investment is company is different than a loan (which is paid back). One is Equity and other is Liability.

I have never seen a need to separate initial investment from later contributions, but see QB does that,

so maybe there is a reason.  Never seen split on any other accounting system.