Roof raise and house windows is the best bang for the buck.
Some trip buses cut every second pillar out and install large 4 foot long sliding RV windows. So therefore cutting out every second rib should be fine.
At your height (6.6) I would not mess around. Do a 24 inch raise, vault the ceiling, and enjoy. You will be able to look out the window standing up vs laying down. lol
When mine is done, I will have a rub rail every 16 inches on the new skinning steel. This will make it hard to tell it was not factory.
I will also have a nice 24 inch by 24 inch window over the headboard of my bed. This window will be installed in the new skin steel.
I will also have a 30 by 30 window at the back of the bus where the door used to be. It will also be over the bed.
I have already installed 6 residential windows in the new skinning steel at the front of the bus. They are two 4 foot high by 5 feet wide, two 4 foot high by 2 feet wide, and two 30 inch high by 5 feet wide.
For reference, my current build.
Also go read as many build threads as you can. The information inside each one in invaluable.