Elliot, Welcome to O gauge and the Forum! You have come to right place! I can write from experience as I left HO and came here 8 years ago.
I like the general concept of your plan. Of course you posted it here for input to tweek or completely redo it. I did the same thing. Others have mentioned the need for access. I advocate the around the walls and peninsula format over access popups or, Heaven forbid!, crawling on top of it. 
I see a great photograph on your profile of what looks like a father and son enjoying time with a steam locomotive. I am thinking you are the younger man with your father, but can't be sure. I'm 63 and am off and on building a layout that is around of the walls/peninsula design. No area will be over a 30-inch reach, and there will be minimal work under the layout. If you are younger and are able to crawl under for wiring and to get to access hatches that is great! Just remember, you may have an accident and not be able to do it for some time, where you could have gotten back to the layout sooner if you had access. I post on this Forum a lot, and many folks know my series of physical problems I won't go into that have kept me from continuous layout building over a 5-year period. That is even with an 'easy access' design.
Keep posting and we will help you in every way we can!!!
