Good morning @Casper Boutens
I know a little bit about realtor branding, so I figured I'd chime in. An IDX isn't necessary for your website, but you are required to display your license number and some basic information about yourself in case you do display MLS listings on the site. Generally it's good practice to simply display that everywhere you can. Once you're a licensed realtor, this is a pertinent requirement. Even if you're uploading your own listings manually, you're still required to display that information.
Giveaways are a great way to grow your following, and as long as the transactional nature stays strictly on the "join my mailing list, or whatever" in return for a chance to win something, you're in the clear. Most conflicts that realtors have to avoid are more strictly surrounding real estate transactions. Another rule of thumb here is to consider fairness in a transaction. If you're giving someone preferential treatment, or giving something away that might be seen as a kickback in return for an offer or consideration on a deal, that's when you might fall into muddy water.
As for website disclaimers, the primary one is the following: An Internet site which consists of information regarding properties which have been listed with a real estate brokerage, the identity of that real estate brokerage or licensee for each property and information related to those properties must be present.
As far as must haves, i'd include a picture, and contact information. Beyond that, in my experience real estate is very much a relationship business. I've met extremely successful realtors with websites that look like they jumped right out of the 90's internet boom days.
I'm not an attorney, so obviously do your own research on requirements for your site.
All the best!