First off.. Welcome to the Dark Side...
Now, let me share some personal experience. I have had Fw tanks for most of the last 35 years. When I decided to go with SW I had already spent many months reading, watching videos and learning all I could. I converted my 55g FW tank to SW. I used most of the same equipment on this tank as I had when it was FW so very little expense there initially. New rock, substrate and lights were all I needed.
Later I got a great deal on a used 180G tank. This setup became a Fish only setup as I wanted fish that I knew would not be suitable for a 55g mixed reef.
Later, after several months of success with the 55 and 180, I decided I wanted a nano tank so I pulled the trigger on a 32g Biocube. This tank has been such a major pain in the umm posterior. I am honestly about ready to tear it down and sell it. The enjoyment from it is not outweighed by the extra attention it needs to keep it stable. You might think that 20 gallons difference is minor, but in this case I can say that YES it is!!
The general consensus here on your question is "Bigger is better" I fully concur. Yes, it costs more to set up, but the stability of a larger system will, in the long run, give you the confidence to expand your envelope. If you get a smaller tank, and spend all of your time battling stability issues, you will very likely become discouraged and quit the hobby.
This hobby is challenging in its way, but it is also quite simple as well. As an absolute beginner of any aquarium system, my advice is to not add to your challenges by trying to start with what is inherently an unstable system right out of the box.
