The important thing is to gain first-hand experience rather than repeating a technique that you don't understand. The techniques were made by humans just like you. You can make up your own technique that works best for you. I think that in order to get a first-hand experience I needed to get very in touch with my body, by doing yoga and deep breathing, etc. Actually, deep, rapid, and smooth breathing is great. Instead of visualizing right away, try using your feeling sense. Try to feel your core. Try to feel the central core of your body right in front of your spine. breathe in strongly energy up from the Earth through the central channel to the top of head. Breath out a fountain from the top of your head that falls back down to the Earth. Just experiment and find what is fun for you. Try adding visualization when you feel more confident. Don't worry about if you are just imagining results at first, just have fun experimenting. Eventually you will get deeper and deeper into it and IT will teach you what you need to know. Let your own Kundalini teach you. Eventually you will need to develop stronger and more stable concentration to hold the subtler energies of the higher chakras.
I never tried closing them, I don't know why one would. Maybe that is why I am so crazy. I feel that the aura itself will protect me from any threat. A strong aura is like a strong immune system. If anyone or thing wanted to get your energy or enter your energy field it would go through the solar plexus chakra, so make sure that one is strong. Or cover it with your hand if you feel someone is trying to get their "hooks" into you. Visualize your aura having a strong, flexible, transparent shell around it when in doubt.

Also, I never visualized flowers. I just visualize dots of colored light, that is what works for me, flowers don't, but that is up to every individual.

You have the best teacher in the world, your kundalini, your higher self, your true self, your still, small, whisper of truth.