The simplest and neatist finish is to have the wall opening slightly bigger than your tank so it can slide right through the wall so it lines up with your wall surface. This means overhanging the tank off the stand by the wall width but allows you to frame the tank against the glass like a wall picture with no gap. The frame conveniently hides all the mess so very easy to finish off neatly (less time, effort and expense).
The other alternative is to have the tank against the back wall and create a recessed frame. This is much harder to do neatly but allows you to have a much smaller wall opening. Could have two openings at different heights if your tank is big enough.
If you don't have access to the back of the tank, you will need top access. If your tank is very wide (over 1.5m) then best to have access from front and back.
Humidity and heat are usually underestimated in enclosed wall setups. Perhaps build in extractor fan(s) and vents while you are constructing.