You can mainly refer from
m980's map if you are interested in iNiS mapping because he's one of the mapper who aims for the originality of the style.
Nao briefly explained the aspects of the style, and the combination of those along the modern styles would make an interesting outcome too imo. For example you can make a map with melody-heavy rhythms without filler rhythms while using modern visual style etc.
One thing that can get added is the placement style which avoids overlaps. As you stated as "opaque 300", the skin left behind doesn't really work with the current overlap styles and rather look messy. Rhythms being less dense than the current period is also a result of the skin, because leaving too many 300s in a short period makes the screen messy and leaves less space to place objects. But since most players use transparent 300 nowadays, you kinda have more option than then.
As the style utilizes copypaste and symmetry a lot, it is easy to complete a map but it is also difficult to create something interesting out of that. So compared to the easy accessibility, it requires a lot of mapping skills to make a good outcome with the iNiS style.