I guess, you can just follow any existing payment extension that is close in approach. Copy it and create an new one.
Many payment gateways similar in approach. But unfortunately, we do not know much about Indian payment systems.

If you are wiling to contribute this module to community, we can help you if you run into issues.

There is no way to do this yet. Currently, Brands and Categories are independent.

What is coming in the future, is an ability to refine product listing result.

We will consider combining this feature together.

Hi James,

You have very good questions. Let me clarify.

AbanteCart was designed to work well under heavy traffic and data load. We do regular tests for performance under different conditions.

To support good performance AbanteCart utilize caching of the data and optimized database queries.

About UI.
Keep in mind that most of the traffic and load will be on the storefront of your cart. There is no heavy an bulky JavaScript for UI that will effect performance of the storefront from UI perspective.

Bottom line, we believe that AbanteCart is capable of handling large loads and volumes, but it is not enterprise solution as of yet.
In any case, we will be glad to resolve issues related to performance if they arise.

We will try to check and come back on this question. Theoretically it is going to work but we need to create a language package with RTL and test.

The best way to deal with changing language text is do this via control panel tools.

You can use global search (admin) right top corner to find text that you are looking for edit, click on the link in the result and edit it.
After you save the result, refresh the page where to expect text to show. Done. 

If you edit the file, you will need to reset cache and reload languages again. This is not desired approach.

Hi James.

Thank you for your warm comments and welcome to our forum and community.

We are sorry for some delayed responses. All members are very busy with new updates and fixes we do on the cart. We work our way to production stable release.

Are you a developer?

You do not need to install second copy of abantecart. After you create and configure the setting for second store in the control panel, you need to point your DNS records for second domain to the same location as first domain.

Hope this helps