Small tanks do not allow much margin of error since theres less water to compensate for mistakes compared to larger tanks. I started with a 55 and I thought that was a bit small. The saying goes "Buy the biggest tank you can afford", I personally do not like the hassle and care of big tanks (or mainly tall tanks where you cant reach the bottom). Good sizes from my understanding are 55 to 75 to 90 and maybe even a 120. Between the sump and refugium if you add one you'll have alot of water to compensate for newbie errors and still have a nice showcase of a tank.