WOWWWW this thread was quite a read!! Holy **** ...
@Douglas Gratz I am significantly less experienced than a large number of people who've already commented on this thread, but I do build homes and have found success doing so. My husband and I are in business together, we are a licensed General Contractor. My husband has design-build experience, so he does the designs and we just pay a small fee for an engineer to review and stamp the plans. We are using our own money to fund the projects, so we have no loan costs and the risk is significantly minimized. If we lose it all, that's all we lose. Nobody's coming to take the house we live in, or any of our other assets if we "lose it all". We manage the projects and the subs entirely ourselves as well, so nobody else gets a cut of the profit. I am also a licensed agent, so I am saving money on commissions as well. We are currently working on my 5th house, and getting ready to break ground in a week or two on my 6th house. The houses we're building are small, but nice. Not luxury or high-end but, nice finishes and in up-and-coming neighborhoods. They are around 1500 - 1600 sq ft each, and our profit per house is in the $90k range.
And still ... with everything I said above, with the amount of experience I have at the moment, I would DEFINITELY NOT feel comfortable taking on the project that you have in front of you!!!! Even some of the more experienced people on here said that the project you're describing would be out of their element. You keep responding talking about how "the numbers work". We have no way of knowing if the numbers work, as we don't have all the data, but I can tell you that IF the numbers do truly work, they will only work if you know what you're doing ... and you don't. You've made that very clear. For that reason alone, because this is YOUR project, and YOU are the one carrying all the risk, and YOU'RE the only one who will be held accountable if the numbers don't work, YOU need to know what you're doing (not your consultant, not your GC - YOU). The only way to know what you're doing is to gain the experience over time. It's just not something you can step into.
The ONLY thing that others have said which I don't necessarily agree with are construction costs. I'm currently building at $130 / sq ft. Granted, we're saving a TON by being our own designer, GC, and developer ... and we aren't building luxury homes, but yeah that's what we're currently building for. Just thought I'd throw that out there.
Also, you said a lot of alarming things in your posts, but here's one that really stuck out to me, which nobody else has commented on - "Comps in the area dont have many homes this large downtown Philadelphia." Why do you think that is? Do you think that the builders and developers in the area just never thought to go bigger? NO!! They just have the basic common sense to know what works and what doesn't. If the house you're building is bigger (and therefore more expensive) than everything else in the area, then NOBODY WILL WANT TO BUY IT. There was a newbie developer in my area who just made this exact mistake. He purchased 6 lots all at once, and immediately started construction on one of the lots. The house he built is huge for the area. It's about 2000 sq ft, whereas everything else in this particular neighborhood is under 1800 sq ft. It's also the only house on the block, so it's surrounded by empty lots and therefore undesirable. He initially listed it at what he THOUGHT was market value, based on the square footage selling prices of other homes, but he clearly didn't take the vacant lots into account, nor the fact that the home is too big for the area. It literally just went under contract after sitting on the market for A YEAR. While all the other houses have been consistently selling relatively quickly for $250+ a sq ft, he had to continue lowering his price to even get potential buyers through the door. The last final listing price was just $180 a sq ft, and who knows what the final offer actually was. You mentioned at once point a "worst case scenario" of the house taking 9 months to build .... the amount of time your house will sit on the market is also a huge factor to consider. Also during this time, when his plan was to sell this house and roll the profits into his next build, he had to sell off the other lots. Or he tried anyway, nobody wanted the lots. I don't know the guy personally. I can only imagine what his finances are like at the moment.
Anyway, as others have said, you seem convinced that you know what you're doing and you're going to move forward with it, so there's nothing left to say except I wish you luck.