How Many Flips In A 9 Inch Box?

about 80-90

Oddly enough this can vary excessively. If your meaning those standard cardboard flips, that is one thing. HOWEVER, there are different thicknesses to those. Some heavy duty ones I've got even have a hard time getting a standard staple through. Some are really thin also. But an estimate of from 70 to about 100 should be OK.

There are numerous methods of storing those coins. The cardboard flips could become expensive if used for just ordinary coinage. If you check with a coin store, coin show and/or even some hobby shops, they usually carry packages of really small plastic bags. Coin sizes. I've found them in packages for small coins, medium sized coins and large. Some have miscellaneous sizes in the package and some are for each size. They are reasonable cheap compared to plastic rolls, cardboard or plastic flips.
With those you just insert a coin or more, bend over the end, tape shut.
I use these for all my foreign coins. I am not a foreign coin collector but people that know I collect coins continue to give me coins from their homelands. Working with individuals from many countries has made my pile of those coins extensive.