This is Dallas from the Shopify Social Care Team. Great question and I'd love to help you out.
Now I'm not from India and sadly I've never been there so I can't say what gateways are the most popular. However, I took a look at the gateways available for India and the gateways available for Australia and did a bit of cross-referencing. There are a few more options, but I've heard other merchants work with PayPal, 2Checkout and LayBuy a fair amount. This will really only come into play if you're ever looking to switch the location of your businesses headquarters to India. Then you wouldn't have to skip a beat when it comes to choosing a new payment gateway.
However, no matter what gateway you choose out of the ones available to you in Australia they'll still allow your customers to purchase products around the globe. If you're in Australia I suggest that you use Shopify Payments though. That gateway allows all of your customers to use it around the globe, plus you don't have to pay any transaction fees so it's a win-win for all parties. Have you heard of Shopify Payments before or is there a reason that you're not wanting to use that option?
Now you're talking about trying to market to a wider audience. Do you have a plan on how you want to go about that? Have you come up with a marketing plan?
Please let me know so I can continue helping you find the best fit for your store and your customers.