You will not find a better bunch of folks that here on LSC. Answers to questions are plentiful and best of all free. Do not be afraid to ask any and as many questions as you like. Someone, or more than one someone will provde an answer.
To assist in getting answers, tell us a little more about where you are and where you are heading with your railroad. Will it be a simple loop to watch trains run around or will there be operations involved? Are you planning a modern mainline pike with big diesels or a smallish short line or narrow gauge with small motive power and short trains? The more you are willing to provide, the better the answers will be.
I will step off into my basic starter advice. Being as you already clarified that you will be running track power, I recommend a minimum of a 10 amp, 18-24 volt power supply. If you are looking for an all in one package, you can’t go wrong with a Bridge Werks unit. They make several different ones, you would need to decide which one might be right for you. My alternative suggestion is a Meanwell 10 amp 24 volt switching poer supply with an external controller. One that is quite popular is the Revolution Train Engineer trackside unit. My club has several of these and they are very reliable.
Layout design - the larger the diameter of the curves the better. Space of course will dictate size here, but bigger is better. Switches is the same recommendation. If you have the space, a wide radius (10 foot diamtere) or No 6 is the best bet.
Track, is a whole topic of itself. Aluminum track is the lest expensive of the three major options. For outdoor use it is the least robust of the three materials, subject to damage if you have mother naure’s visitors with sharp hooves. Although aluminum is a good conductor it also oxidizes the quickest and aluminum oxide is not a good conductor. Electrical connections (track joiners) will be a maintenance issue to keep the elctrons flowing. Brass is the next choice, and I consider it the best. It is middle of the three materials in cost, is middle in durability and still a good conductor. Joiners will stay reliable longer. Brass will need occasional cleaning (a scotchbrite on a sanding pole works well) but is not over burdonsome. Stainless steel is the costliest by far and in my opinion does not offer sufficient advantage over the others to justify the cost. Stainless will nearly never need cleaning, and is the most durable. But is is the most difficult to work with. Requires heavier than model work tooling to cut, will not take standard electronic solder for electrical connections and is probably the least available material.
A trip to the bookstore to purchase “Garden Railway Basics” by Kevin Strong would not be money wasted. He covers most all of the basic questions beginners have and frequently has an opinion on which is best and why.
Welcome aboard this ‘crazy train’.