That spectrum loco is prabably pretty big, anyone here sure that it will make a 4x8'? Anyway, not much to add to the advice given, Im only a few years really into modelrailroading so here is what I can add to other peoples comments.
Walthers kits- my favorrite, they have the widest variety of what you can make, and are a good company to work with, the cornerstone series is also priced good in my opinopn, except for the harder to find kits. Take you time, when working on them and they can be great.
Athearn blue box kits- Ive never built many, but they are priced good for what you get, but as always, take your time, they tend to be irritating when you get stuck on that ONE step that wont work as I always find. Walk away and come back afterr you cool down, they are not fun kits when you are mad.
DPM structures- Ive only built one, they are like the athearn BB of structures, most what I said above applied to the DPM kit I made, but with weathering and detail, can be made to look like some of the very high end kits.
I hope that helped some too, but just do what your doing, go to the local hobby shop and look around, I like to try something new everytime I go if I can afford it.