Hi, I started a SaaS and started selling with no actual product.
In order to understand what to do.
1. Who are your early adopters ( the ones that are suffering the most because you don't exist).
2. Understand their Real problem and them promise them something.
3. Use things that alteady exist and put them together to make that promise realitu for them.

This is utterly important because you'll learn what to build later, adjusting the SaaS as you are the solution, then you build it.

Now a big thing is PRICING most of the time this is something that gets us all stuck.

Here is my approach.
Think what is the maximum you can change for what you are promising. Try not to think on how much it will cost, but how big is the problem that you are solving. The charge it. By putting a number you'll be able to start the conversarion you need to have with your early adopters in order to understand the value of your SaaS.

Hope this helped!
If you want to tall more give me a call.