Alright, let's slow down a bit. One really big piece of advise comes first and foremost: Test the tank for leaks. See if you can find a space outside that you can place the tank for a couple of days and you don't care if it gets wet. Hopefully, you will get a couple of sunny days. Lay down newspaper, fill the tank with a hose. If this does not work, a 45 might fit in a bathtub (but this could be difficult). Please please please do not fill the tank in your house without leak testing. 45 gallons is a ton of water. I just bought a second hand 20g that had a leak, so it's in a closet right now instead of on my shelf.
Ok, that was the most important thing. Next:
Cleaning the tank: Don't use soap, almost impossible to get rid of once it's in there. Hopefully, no one else used soap either. As fshfanatic said, regular white vinegar is great for cleaning the tank, both inside and out. Give it a good scrub with white vinegar, being careful not to press too hard on the glass. It probably won't break, but you don't want to cause any separation on the silicone seals either.
At this point, pause, reflect, then think about what you want to do
How much money, time, energy, and enthusiasm are you willing to put into the tank? This hobby, at it's highest level, is extremely expensive. It doesn't have to be, but it's best to make a decision about that before you go off buying stuff. I'm not gonna lie, if you get into this hobby, you will without a doubt buy something you don't need just because it's cool
Draw some sketches, come up with some ideas about what you want your tank to look like. Here are some places you could get ideas from, but some of the best tanks don't look like these at all:
Here's an article on basic aquascaping:
This will be one of the many expenses. Here are two good articles about lighting:
The amount of light you need depends on the type of plants and the rate of growth you want. Many plants can grow in lower light, just at a slower rate. Other plants may grow in lower light, but in ways that you don't want them to (i.e. growing very tall instead of staying short). More light = more growth = more co2/fertilization/maintenance (cost).
Now, when people say 10000K or 6700K, this is the color of the bulb, not the amount of light output by the light. I believe that plants grow best under 6700K bulbs. The wattage is a different story. You can have bulbs with different color temperatures in the same wattage light fixture. While not quite accurate, you can think of the wattage as a measure of how "bright" your light is. The articles above explain why this isn't always the case. Anyway, one of the oldest rules which is no longer widely accepted is the watts per gallon rule. It is a very inaccurate and rough estimate of the amount of light you have. But, it's a start. The amount of light you need is, again, determined by how you want your tank to be. Around 2 watts per gallon is a reasonable amount to shoot for. Some people can do great things with lower light, some people do great things with higher light. Just keep the electric bill in mind
The voltage is the potential difference across the two holes in the wall socket (not really, but that's a good enough explanation for our purposes). All US sockets are about 110-120 (They are the same socket, but the labels on appliances might vary). Your electronics won't fry if they're meant to be used in this country. So, don't worry about that. In the same vein, 55W and 65W bulbs are pretty much the same thing too. This will come into play later if you choose PC lights.
Substrate: Many people do fine with plain gravel. It's not as nice to look at, and certain plants require smaller grain sizes to spread, but there isn't anything inherently wrong with gravel. Virtually all aquatic plants can feed from their leaves anyway, so whether the substrate is nutritious doesn't matter too much. Aquasoil is the best, but it is expensive. Other choices I recommend you look at: Flourite, Eco-Complete, SMS. Please note that Soilmaster Select (SMS) is not sold as an aquarium substrate. It is marketed as turf conditioner for athletic fields. It comes in red or charcoal, and it is getting hard to find, since one of the main distributors just stopped carrying it. I like this best because it is really cheap, and just as good as Flourite.
Rocks: First, do an acid test to see if your rocks will alter the water chemistry. It's really not as scary as it sounds. Just put the rocks in a bucket, and pour some distilled vinegar over them. If it fizzes, your rocks will alter the water. If you are paranoid, you can look for muriatic acid at a home improvement or pool store. Home depot might even have it. Boil your rocks. You can just boil them for a couple of minutes. All depends on how paranoid you are. If they won't fit in a pot, bake them.
Plants: This might be the first thing you want to do, actually. Not buy them, but decide what you want, since it will determine your equipment. This tool can help you figure out what plants you want: http://www.aquaticplantcentral.com/f...c/plantfinder/
Filter: Again, this varies with what you want in your tank. For planted tanks, canister filters are best. This is because they do not disturb the surface much, and won't cause injected CO2 to leak out. However, if you have a low light tank and don't need to inject CO2, you won't need to worry about this. In that case, just a HOB/power filter is fine. I would avoid under gravel filters. The brands and makes should be decided later; there are plenty of arguments about this
CO2: All plants benefit from the addition of CO2. However, it is really only crucial to add CO2 in moderately high to high light tanks. There are two main ways people do this. One is known as DIY CO2. Using yeast and sugar, you generate CO2. The other is pressurized, using a CO2 tank, regulator, and needle valve. Pressurized costs more initially, but if you plan on having the tank for more than 3 years, it will be cheaper in the long run. It is also very difficult to get enough CO2 using DIY in a larger tank, especially with high light. Sometimes, depending on the plants and light you have, you may be able to supplement a lack of CO2 with a plant product called Flourish Excel. It is a source of organic carbon that also acts as an algaecide. The carbon is in the form of a compound that is some intermediate step of photosynthesis. Some plants are able to use it. Some plants are sensitive to it's algaecidal properties (particularly vals).
Fertilization: If you have high light, you will need CO2. This means you should be prepared for a fast growth rate. Your plants will need to be fed. Macro nutrients, also known as NPK (Nitrogen, Phosphates, and Potassium) can be thought of as plant food. Micro nutrients, also known as traces, can be though of as plant vitamins. Both will be necessary if you have high growth. Fish waste can help provide some of the macro fertilizers. It is important that you have enough of all your nutrients. Plants need to have enough of everything
in order to thrive. If something is lacking, the other nutrients will not be used. Instead, algae will use it, and grow and infest your tank.
Phew! I know that's a lot of info, but it's really not as complicated or hard as it sounds. Welcome to the hobby as well as the forum!