ouch, yeah don't listen to that.
they are right about the filter. Bettas don't need one. But I recommend one in anything 5 gallons or more. Makes it way easier to clean. Once it's cycled, do a 50-75% change once a week and you're good. The flow might disrupt your betta. But all you have to do is put a filter sponge on the output with a rubber band. Voila! No more flow. :)
You also don't need real plants. Fake are fine. Personally, I love real plants. I have them in my 5, 10 and 29 gallon. They're gorgeous and fun to have. If you do decide to go with plastic, use the panty hose test. Take some panty hose and run it over the plant and if it snags, it will rip your bettas fins. So don't use rough ones.
Driftwood can change pH levels, but not too much. Bettas can adapt to pH well. No reason to not get it.
YES YES YES get conditioner. It gets rid of heavy metals which are lethal. This is confusing, cause a tank can't cycle without a filter, and they recommended you don't get one. Weird. And don't cycle with danios. You can cycle with your betta, just do bigger and more frequent water changes til its done.
Don't do any 100% changes. A cycled tank converts ammonia into less harmful stuff. do a 50-70% change every week once it's cycled. Bettas are hardy, but that doesn't mean they don't thrive in a clean environment.
And don't let that make you never go back. Get legit info and use it. Just don't take their advice. As a general rule, pet store employees anywhere don't know what they're talking about.