If I$\text{'}$m asking individuals to fill out a form on my site so that I can email them, what information should I collect in order to begin sending those emails?

You should gather as much information as possible. For example, ask for their name, email address, phone number, current address, price range of their current home, if they are looking to sell, buy, or both, and what their budget is$.$

You only need to ask for their email address. Then include a check box that indicates their willingness to opt into your emails.

You don't actually need a form. Simply include a QR code visitors can scan that redirects them to your landing page. The QR code technology will automatically pull their email address.

You can just ask for their phone number. Then text them with a link to opt into your email marketing.