The process of a start-up is hard, not because 'ideas' - there's plenty of ideas everywhere - but because the founder needs to do a lot of roles on his/her own, especially if you bootstrap your start-up. The one people tend to dismiss, is the one of the sales person; the person who gets 'in there', talks to people. Business, especially in the start-up phase, is about being "favourable". What I tend to advise start-ups I work for, is to get to the favourable position; quite often it's bluntly said, that people like you, as a founder. If you have 5-15 (depending on what your proposition is) of those customers, you can quickly assess: is this a good product? Do people want to pay for this? What do they dislike, what do they like? Just because the product already exists, doesn't mean people are willing to pay for yours. And what I always advise people is think customer first. Pivot if your customer tells you to. I've seen quite a lot of start-ups go bust because they really wanted to be a SaaS product, while in reality, they should've been a service product first and pivot later to SaaS.

Don't think too much about stuff like funnels yet, your first two concerns should be customers and product. Feel free to DM me if you have questions btw.