What is the size and arrangement of your currently available space? I don’t think you’ve ever answered that, and it matters. For a younger person, life will entail many changes in the coming years. Can you be assured of an 8-foot-wide, 25-foot-long space in the next few years – it will take a while to build something this large and a long time to scratchbuild the structures (which mostly aren't off-the-shelf footprints).
What I want to do is build the SIW as is and then after I am finished begin stage two which is the rest of the layout. Would that be a good idea?
Not to me, but that’s just a personal opinion based on my experience. Every layout is a reflection of the builder’s unique interests and circumstances. Outside of that context, any published layout may not be satisfying to someone else. There’s nothing magical about a published track plan.
According to the article in the March 2008 MR, the original builder of that layout was interested in scratchbuilding steel and other heavy industry structures of the early 1900s (when locos and rolling stock were smaller than in later eras). From your other posts, this doesn’t seem to match your interests. The tight curves and turnouts in this plan as drawn will limit what you can run on it in later phases.
Because he started with an HO 4X8, the original builder was a bit hamstrung as he added to it. As noted many times in this and your other threads, if you have enough space right now (and in the immediate future) for this big rectangle and its aisles, you certainly have room for a different layout that wouldn’t be so restrictive of the rolling stock that could run on it.
But if you don’t have that space now or in the immediate future, in my humble opinion you’d be much better off with a smaller layout that offered a broader variety of opportunities and challenges (such as building grades) and could be built to the point of running trains and completing some structures and scenery before you move on to college or other later pursuits.
Also since I am horrible at track planning could you make a rough sketch of what you are suggesting?
Sorry, not able to help there. Perhaps someone else will, but I encourage you (and them) to consider what best meets your interests before going too far down the road with this specific (and specialized) layout.