What's the best payment gateway and why?

If you haven't fully tested your app with the 100 individual accounts Apple allows you to test via TestFlight or Hockey, then I'd suggest you should test thoroughly with your email list before launching to the app store. Things to look for at this early-stage: Activation and Breakage Points: From app download to user onboarding, where are people getting lost? Your goal is not only to have them download the app, but complete whatever steps for them to become your user. Optimizing the flow to ensure maximum conversion is a key first step. Engagement: How often are they completing the tasks you deem most important based on your business model? How can you increase this number? User Understanding: How clear is the app's UI and messaging? Where are they getting lost? Virality: While true virality is hard to measure at this stage (given the constraints of pre-launch testing), you can evaluate the potential effectiveness of any distribution tactics you might employ (contacts, OAuth's etc) in terms of user opt-in and conversion issues. Real analytical data is easier to interpret than user interviews but there is a such a treasure trove of good customer development intel from customer interviews. Those first 100 people who download the app should be personally interviewed about their experience, what they like, how much it solves their problem, how much of a problem that is for them in the first place and so on. Before you go live in the app store, I highly recommend you max out your installs in a private testing environment. I'm happy to talk this through with you in more detail in a call.

there is Balanced, Dwolla, Braintree but none of them seem to work in India yet.

The ways I've done this in the past are 1) Find some customers that are willing to hire you (or your product) but know that you'll only be free nights & weekends to support/work with them. 2) Find a "partner" (co-founder or other) that's got a flexible schedule that can help build the business while you're at work. 3) Block out nights, mornings and weekends to build the business till you have enough orders to cover 50% of your salary. This might mean 7pm-11pm most nights, and 4 hours each day Sat & Sun. Make progress (sales $$$) and momentum. All that being said, it's risk reward. Sounds like you want to avoid taken the risk, and I get that .. but the upside is always smaller. Unless you put yourself in a position to have to succeed (ex: quitting your job) then you may never make the scary decisions that are required to build a company (like cold calling, going in debt, making a presentation, etc). I'm on company #5 with many other side projects started nights & weekends .. so I get it - but don't be afraid to bet on yourself and go all in.

A generalized question can only get a generalized answer. The most significant accomplishment is validating that the product you have built is a fit with your target market. This is demonstrated primarily by engagement (the people who sign-up or who previously visited, continue to return) and secondarily by growth, ideally based on word-of-mouth or viral growth but effectively converting paid traffic is a great second prize. Other significant accomplishments include: Not running out of money Recruiting and retaining great talent who believe in the founders' vision. Your loved ones not thinking you're as crazy as they thought you were a year ago. I'm happy to talk to you in a call to give you more specifics about what you want to set as your goals more specific to your startup.

The ideal way would be to hire the engineer while the project is still under development. You and the engineer should follow up with the outsourced partner in the process. This will give hold to the engineer and later more staff can be trained in upgrading or follow on versions of the product/service.