If you can access your store and log in from different IP's then it's more than likely an issue with your internet provider and not Shopify in this case. Would you be able to reach out to your internet provider and check for me, please? It could also be a browser cache issue. It could be worth clearing your browser cache and seeing if that works too. Let me know when you try either of the above and the results you get.
Yes, I know what you mean. You can address this by making your primary domain the one without the "www" at the start of it.
The best way to be able to get a landing page and customize it would be via a page-builder app from the Shopify App Store which allows you to create landing pages while keeping the site open. Check them out below:
The password would be completely up to you and generally temporary as you would make your store live in time. There is no best or worst password, but one you are comfortable with and can remember. You can see the guide Shopify has for this here.
|an hour ago|