Great advice so far; I’ve seen others success with the Hipargero and I am also a big fan of SB Reef Lights.
The downside that I know of SB Reef is that their lights are inefficient, so they produce more heat. That said, they offer great power for your price, offer a 2 year manufacturers warranty (and the owners claim they treat as a lifetime warranty), and for simple things like diodes needing to be replaced they will do it at cost (not for profit). If you’re looking for something affordable; these are the two brands I’d look at. So you’re on the right track!
And not to rain on your parade; another concern with beginners hoping for SPS in a Nano will be temperature fluctuations. 20g is quite small and even with a heater, it may be challenging to get many SPS to grow. I suspect you’ll have difficulty with various Acroporas; this can mean that they won’t survive, or that they will simply not grow or grow even more slowly.
My advice when a person is considering getting a first reef (or any) tank is; don’t consider your tank size based on their gallons. Instead consider tank size practically by basing it on the area they will take up in your home/office.
For example: let’s say that you have 2 feet of space along a wall. Many people will think “I want a tank. 20g tanks are that size. I will get a 20g”. With this hobby, you will want more space very quickly. However, if you instead choose to dive a little deeper, you can find larger tanks fit this same footprint (we even had an awesome custom 80g tall tank that’s 24” wide). Every extra gallon you can accommodate will mean potentially more fish, more coral, more stable water, and so better growth. Just something to consider, and it requires introspection to your long term wishes. In short; Nanos can be more challenging, more work, and leave you wanting more. That said... maybe a Nano is right for you after all! Only you can best judge that.