GST Materials - Ensuring im accounting everything correctly

Hello, quite new to this so I’m looking to make sure I’m doing all this correctly.

Firstly, i run a business that does property maintenance. With 2k Owner introduced funds - Which equates to 2k Cash at bank

For simplicity stakes, I’ll run through one invoice etc.

Job:1 is install a man-hatch into a roof.
I pay for the man-hatch up front out of the 2k owner introduced funds. Man hatch cost $30.91 excl gst - $34.00inc gst. I import my bank transaction for this, and reconcile the transaction as a cost of goods sold expense.
Is expense the correct location for this?

I invoice the customer for the installation of this man hatch. and also the purchase. I input the installation under the sales account, and i input the man hatch under sales as well.
Man hatch cost: $34 inc GST - Just wanting reimbursement for the product. No markup
Installation: $86inc GST
Is this also correct way of accounting this?

Assuming this is all i input (Leaving deductions out such as fuel etc to simplify)
Should the GST Bas Calc be this for the above:

1A GST on sales $

1B GST on purchases $

9 Your payment $

Just making sure that materials i use to complete a job are being correctly input.
Any response would be great.

What you have drafted sounds okay, but do you need to breakout the Man Hatch on the sales invoice ?
Why not just invoice the installation as 120.00 ?

Another option, if you are just passing trough the expense is by using Billable Expenses.
The purchase is put to Billable Expenses instead of Cost of Sales.
But when it comes to the Sales Invoice you need to invoice the Billable Expense first prior to adding the installation fee. The following link is to the Guide