I love the pictures and the talent of this BBQ build. I have built a few and used hundreds of different pits over the years----and sometimes see small problems. It is dificult to build a pit that can be used for grilling, smoking, and electric smoking--but I think it can be done.
The first problem I see has been mentioned by someone else. To achieve proper grilling temperature either the grilling surface must move up or down or the firebox must move up or down. If neither move then a waiting time is required to start grilling until the coals are "just right" and then the coals only stay "just right" for a short time. If the grill surface is close to the bottom of the firebox then stick firewood can not be used--only small amounts of charcoal.
If grilling is the only type of cooking done on a pit such as a "Santa Maria" style pit then grease drippings simply drip on the fire and burn up.--However if the pit is closed down and used as a smoker then grease will drip on the coals and make smoke that is not desireable in smoking. If the coals are placed far to one side --and the meat far to the other side--then grease will drip and accumulate on the bottom of the firebox--and possibly cause a very undesirable grease fire.
An electric burner with a chip tray can work good for smoking--but only IF that is the only way the pit is ever used. Otherwise ashes from charcoal or wood will cover the electric element--or grease accumulates around the element. Anything used for smoking should have a method for grease to drain off.
Also when building a pit it is important to remember that you will be the person cleaning it--make adjustments for ease of cleaning.
BBQ folks have been trying to reinvent the "perfect" pit for years---but each seems to have it's own strengths and weakness's Please do not make the mistake of trying to make a pit so versatile that it's problems outweigh it's strengths.
I hope this pit does everything that you want it to do because it looks beautiful.