In general, you are never going to want to reinvent the entire wheel. I would say anything that is "core" to your business is probably best to build in house while you can use existing saas to help with the rest. Lets break this down a bit for your use case :

- Local delivery: There is quite a bit of offline work involved in partnering with the companies etc to deliver for them (i m guessing, not an expert in local delivery). So just wanted to throw this out first.

- Delivery logistics using software: This is probably the core of your business in my opinion. So you may want to build this in house. For example, the entire UI/UX that a user will face to get local delivery via your app/website.

- Other things like payments etc, use existing tools of course like stripe etc.

Think of it this way. If the "SAAS" that you use instead of building in house goes out of business, will your business completely collapse or will you be able to move on to something else (yes it will still be painful i m sure) ?