How do you keep a SaaS project in its validation phase flexible?

You're creating a product, maybe for your new startup. You have limited resources to build that product: not much time, not much money, and not necessarily much brain power (you're not stupid, you just don't have a dozen engineers available for you 24/7).

Plus, the product you're building will have to ba validated to see if users like it. So you'll need to be able to analyse specific metrics and be flexible: roll out new functionalities very quickly, and delete or update old ones.

What strategy do you follow? Do you hack shit together or prioritise high quality code, making it more maintainable in the future? Are there any software architecture principles you'll follow? What about security? How important is it to you at this stage?

I'm asking this because, at the company I work for, there is almost no flexibility at all in the engineering process: we can't take any decision (even the most unimportant ones, it's ridiculous) before spending sometimes hours discussing it in meetings with everyone else in the company (thus slowing down other projects), and everything has to be thoroughly documented. In the end, I've spent 18 months developing a new product that should've taken me no more than 2 months... and it's not finished yet.

Please feel free to give your opinion on what is, to you, a flexible product or engineering process, and how you guarantee that the next product you'll build will be flexible.

Hopefully we can exchange interesting thoughts and articles!