I’ll take a crack at it
Do you want to run on batteries or on track power? If you put batteries and remote control in the trains, you can get away with cheaper aluminum track or brass track with no worries about conductivity. If I were starting out and was committed to running on batteries, I’d go with aluminum track
If you’re going to run on track power brass is relatively cheap and easy to find. I have 90% or so brass on my layout. I have a mix of Aristocraft, LGB and AML track. The downside of brass is it oxidizes and needs cleaning. It’s not that big a deal–I just run a track cleaning car around. The more serious downside is that you need to worry about maintaining track continuity. I put some anti-corrosion paste in all the track joiners as I laid the track–it makes a big difference. You can use “permatiex anti seize compound” from the auto parts store. As time went on, I added the more expensive “rail clamps.” You can buy track in stainless steel, and it needs less cleaning. I use track power, and brass, and it works well. If I had the dough, I’d redo-the whole thing in stainless
If you care about accuracy you will want code 250 rail. The standard brass G guage track is “code 332,” and it’s very durable–kids can walk on it, no problem, adults can too. But it’s way too tall to scale out accurately. If I were really concerned with accuracy, I’d buy stainless or brass code 250 rail.
Where to buy it? There are a bunch of online retailers but shipping is expensive. I plan to wait until the East Coast Large Scale Train Show to buy track. Stuff is on sale there and there’s no shipping but the show is an easy drive from my house.
I’ve had very good luck with Ridge Road Station and with RLD hobbies. Trainworld also has good prices and ships fast.
You can find used track on ebay and sometimes in hobby shops. Just watch out that it’s not too worn–the curves will show wear and they can wear out
If you want to save money, but it all at once. Aristocraft track is excellent and they have a deal where if you buy four cases of track you get a fifth box free. It’s still not cheap, but if you can swing it it saves money. You might want to invest in some track planning software
It’s a great hobby