To solve the custom field dropdown doubling, you MUST disable the "Use jQuery chosen for dropdowns in FE" option from
VM Configuration >> Templates tab. So, materialMart will be alone to control the dropdown selectboxes.
I am sorry to hear your thoughts about MaterialMart. But the point is, MaterialMart is much more advanced template comparing to CleanMart. It offers much more features, almost double. MaterialMart touches almost every single element of Virtuemart Component (while CleanMart only styles the main UI). But this comes with some consequences like you have experiences. The "CONFLICT". Sometimes, you have to disable some settings from Joomla and Virtuemart to avoid those kind of conflicts, so MaterialMart won't conflict with the existing feature. For instance, that "custom field" doubling. It has been declared in the tutorial.pdf that you should disable that settings. But i understand, it is always boring to read tutorials :D:D
MaterialMart also gives too much freedom to developers to customize, and edit the layouts the way they want to. It has well organized folder structure, has some custom functions to override the existing VM functions; but something those custom FN generates some error messages in some hosting, in some situations (like the problem you are having with the manufacturer logo -- but if you upload manufacturer logo to every single manufacturer you have, and make sure you upload valid image file (not pdf or broken image) and enable the "show manufacturer logo via "Flexible VM3 Template" plugin, then you shouldn't experience any problem displaying manufacturer logos)
2- To enable the product availability logos, first select an availability option from the product page (in VM Backend) and enable this parameter: "Displays 'Notify Me' instead of 'Add To Cart' button" from "VM Configuration -> Shopfront" tab.. This is the restriction that VM has, it has nothing to do with our template (it is the same in CleanMart too)
4- You got this message: "You do not have any category. Please add at least one". only if you don't have any published category or you use a 3rd party plugin to manipulate the category file (and your case is the 2nd). To the categories' sublayout, we just add a "else" condition in case no category is found, because Virtuemart shows blank page if there are no category. But since you are getting this error message (because you are using a 3rd party extension, CustomFilter Pro), then you can try disabling the "else" condition from the bottom of the page (and make that page works just like official VM component)
Open this PHP file:
/templates/YOUR_TEMPLATE/html/com_virtuemart/sublayouts/categories.php
navigate to the bottom, and find these lines:
<?php } else {
echo '<h3 class="mt-4 mb-4 font-light text-s-center">You don\'t have any category. Please add at least one.</h3>';
}?>
and replace those 3 lines with this:
then you should never see that message anymore.
Regards.