Early Marketing for a HW Startup

Hello
I am building a hardware targeting cattle farmers. I almost have the BOM with a rough prototype done (still have couple of things that need modifying and re-testing). I built a landing page with the option of registering an email. As expected, no traffic to my page.

My question is in regards to marketing. I am more of an introvert. I keep hearing that i need to start collecting emails for marketing. Start early they say.

But what do you want me to say to potential customers? please visit my website and register? I dont have a photo yet, but it is coming? I don't have a date yet, but trust me, I will make it work?

It is hard for me. I prefer to have at least a demo or a video of my product that i can show and then I will have something to talk about.
Are my thoughts correct?
I would really like the opinion of someone that did this? how early should i start talking about the startup or advertising it?
What do you suggest I do in this regard?