If you're a beginner and you're looking to get an aquarium, I do recommend getting something on the small side, maybe a nano-aquarium and something that's turnkey, like a complete setup. There is the general rule that the larger tank, the more forgiving it is and the more stable it is. Remember, with an aquatic environment, the more water you have, the more resistance you have to fluctuations in temperature, pH, even waste levels can fluctuate in very small bodies of water. The larger the aquarium, the more stable the environment is and the better, the more success you'll have for the tank's inhabitants.
However, a larger tank does require more time and more money to maintain. It's going to have a higher electric bill, materials for the tank are going to be more expensive. For all these reasons, I do recommend getting something that's not too small, but not too large; maybe 20 to 40 gallons, in that sweet spot. Maybe 30 gallons and a turnkey setup. Most stores sell complete setups nowadays that have the tank, the lighting, the filtration, everything integrated. A lot of them have them on just one plug so you don't have to even have 6 or 7 plugs, you don't need a surge strip anymore; just one plug. Everything's designed to work with everything on that one system and this will reduce a lot of the frustration that's associated with picking the right filter, the right air pump, the right heater, the right lights. Sometimes some of these components can be undersized or oversized resulting in mismatches. Going with a turnkey setup, I think is key, and there's so many available right now.
This hobby has exploded with the nano-reef aquariums. Now it's at a point where you don't have to be a scientist or a real reef hobbyist to have a lot of success and enjoy this hobby. You can be just an average Joe going into an aquarium shop, buy a turnkey setup, follow some advice, get your basic supplies, and have a ton of success.