How to set product prices and shipping costs on Oberlo?

[VMAD]

Hi there, 

Not sure if this is the right topic, but I have a few questions regarding the setting of product prices & how the shipping costs come into play in the process. 

We will be selling both dropshipping products as well as products that are made by us on our store. 

FOR DROPSHIPPING PRODUCTS - SHIPPING METHOD

One will need to select this portion "Shipping Method" as shown in the below screencapture.

It shows Singapore as a default because we are based here. However, we are looking to also avail this item for shipping to SEA countries.

May I know if the destination country or rate is fixed once I set it here? And how will the rates change if my buyers are not based in Singapore?

FOR DROPSHIPPING PRODUCTS - PRICE CALCULATION WITH SHIPPING COSTS

From what I understand, my selling price is set by:
Cost + Selected Shipping Method (to country) + Mark Up

However, I tried to do a trial Cart Out & realized that it doesn't add up. E.g: my eventual cost would be inclusive of this "Shipping Method" + another shipping fee (standard/expedited). 
Does this mean that I'm double-charging my customers? And which courier service is selected for that standard/expedited shipping? Is it also my selected option that I've set at this step in Oberlo?

And if I would like to totally exclude adding the shipping cost/method choice at this step, and let customers select a couple of options (Maybe AliExpress or J&T) at checkout, how should I go about it?

FOR PRODUCTS MADE BY US - SHIPPED FROM SINGAPORE

For the products that we will ship from Singapore (local or international), we will have 2 options for shipping. 
For local: Self-Collection & Delivery by a 3rd party courier service (not listed on Shopify). 
For International: Also by a 3rd party courier service (not listed on Shopify)

These products will be picked up from our warehouse by the courier & then distributed. We have the rates on hand and will be able to key them in accordingly.
However, when customers Cart Out, how will we have set this option for them? 

Thank you in advance to anyone that can help to offer some insights/steps for the queries that we have. Thank you!

- The VMAD crew