Welcome. I don't want to dash you with cold water right off the bat, but you should try for learning and fun, also your stress relief, without the expectation that you will "...do it right..." What you take for doing it right in the next four months won't be what you take for doing it right next year because of changes to your preferences as a result of the learning this time around.
That's not to say you should begin to acquire a PhD in rail modelling so that you make few mistakes. We can help to guide you to acquire the tools, materials, and rolling stock you are likely to find most useful based on some exchanges of information. For example, why the 4X8? I realize it is the simple standard, but these days it mostly pertains to people going into N scale because it's a much better fit. You can get a lot of great fun and modelling into a 4X8 if you elect to go N scale. Just a thought for starters. For HO these days, the trend is to somewhat wider curves than in the 60's and on up to the late 90's. Instead of the standard 18" radius curves, most are taking 22" as their minimums so that things run better and look better....more reliability, fewer derailments, the locomotives look more realistic going around curves....that sort of thing. If you opt for wider curves, and have the space, you'll be glad of the extra room. If you remain with 18" curves, you can fit it on a sheet of plywood, but you will be constrained to a figure 8 or an oval with some sidings and industrial tracks. Those get old too soon. Just sayin'...
What era? Modern, say from 1990 on? Maybe from 1970-1990? How about just post-WW II, or maybe the Dirty 30's? Some like the Olde Tyme railroading from 1885-1900, or even Civil War. If you can think about that, it will save a lot of unnecessary buying and selling. It affects your structure purchases, whether kit or built-up. Do you want a 1880 warehouse on your 1990 layout? It would look a bit out of place.
Another question - are you aware of the new way of controlling trains? It is called DCC, meaning Digital Command Control. Each locomotive needs a small computer chip in it to control the lighting and motor. Some can make modestly realistic sounds through small speakers. The beauty of DCC is that a scale-specific voltage is always applied full-power to the rails. The trains will sit on those powered rails until you tell the decoder chip to move the locomotive. If you power the rails in the older DC that you are familiar with, all motors begin to turn and the lights begin to brighten...remember? Not any more. You can make two different locomotives move in different directions and at different speeds, and one can have its headlamp off while the other's is lit. Much more realistic.
i have given you lots to consider, so I will stop.