Its built to last and its a great project! I do like the idea of contrasting color for more character and clearly the oak tops should be the portion left natural (high gloss black works very well if your décor calls for it), Im not sure whats going on the upper tier but small gussets are probably called for either way (if they are not their already), if you enjoy this as a hobby your going to have a ball... mortise, rabbits, tounge N grove is your next step. Through mortise on the upper tier leaving a contrasting natural wood showing would not only remove the need for gussets but it would start making the work more like "art"... I love the idea of name, date, etc. on things. I know the things my dad built but my kids or future generations do not... im going to have to mark them pretty soon for fear my grandkids might sell them for $5 at a yard sale
EDIT: just noticed the finished pics... very nice
time to think about your next custom piece!