[4WheelVFR]

You're definitely not barking up the wrong tree. Many studies have proven that aquariums are very helpful in lowering blood pressure and aiding in relaxation. You're also right that aquariums are like humidors, where a larger environment provides greater stability. A 29 or 30 gallon tank is definitely a great size to start with, although if petco is still doing their sale, a 40g breeder tank is a great size.
As far as equipment goes, here's a simple list.

Hang on the back power filter-very easy to setup and maintain, relatively cheap, usually extremely reliable, and probably the best filtration imo for small to medium tanks.

Heater-Ebo Jaeger makes the best imo, titanium heaters not worth it unless you have very large tanks....i still have glass heaters on my 1000g, albeit connected to a controller.

Air Stone and pump-I used to think these were outdated and unnecessary, but on any tank I've had one on, my fish seem to like it.

Lighting-LED all the way. A cheap led strip is good enough for a small tank and they use hardly any electricity at all. T-5 is next best.

Gravel Vacuum-for siphoning old water from the tank when doing water changes.

Dechlorinator-neutralizes chlorine and chloramines from your tap water. Prime by Seachem is the best, but any will do probably.

Food-New Life Spectrum is what you want. Great food and available in any size.

That is really all the equipment you need. You may also want a top for the tank and then there's all the gravel/sand and decor. It may sound intimidating but is not bad at all. Many petshops have aquarium packages where everything comes together. Craigslist is also an excellent place to find whole setups, often much cheaper.