As a startup, when transition to deployment, how can I scale up in terms of development, size, and new features in a low cost way?

I think the keyword is to be efficient. The requirements need to be clear in order for developers to be efficient with their work. having a clear development goal and target help them manage the work and expectation. And for developers, they need to be efficient with their work by using tools like task management, unit testing, automation etc. By using the right tools, fewer bugs and time will be spent to debug and fix things. More time to focus on what new features to do. By doing so it would allow startups to manage cost well and burn through hiring a very big team

In my opinion, when transitioning into deployment, focus on 'perfecting' existing product by reinforcing your product USP, listening to customer feedback, working out all the bugs/kinks etc you may find valuable information and implement cost efficient + high value solutions.

naturally, you will come to a point where it is viable to scale which requires different skill sets, leadership styles and features...

Look into your company's ecosystem, who are the strategic partners that might benefit you? Most strategic partners will help your company grow and penetrate the market in a faster way. But always remember that it must be a win-win situation for both side. The last thing a strategic partner wants from you is you are just trying to leverage their bigger brand identity for your own merits.