Hi,
Why not use the standard joomla login module on your website ?
If you don't see the prices with tax on the products listing/page before the checkout, then, you should make sure that the "main tax zone" that you configured in the configuration is taxable. Otherwise, until the user enters his address, the system will use that main tax zone to see if it needs to display the prices with tax and it won't since you set it to a zone where the tax is not applied.
In the listing_price view file, you will have to swap the line:
echo $this->currencyHelper->format(@$price->price_value_with_tax,$price->price_currency_id);
and the line:
echo $this->currencyHelper->format($price->price_value,$price->price_currency_id);
and change the line:
echo JText::_('PRICE_AFTER_TAX');
with:
echo ' with taxes)';