From my POV the main drawback with a full-spectrum conversion is that you'll always be using a filter of some sort. I had a full-spectrum Fuji bridge cam for awhile about a decade ago, and found shooting with no filter to result in soft-ish images with muddy tonality. I don't recommend sans-filter pic taking if you're considering that as an option. On the plus side full spectrum lets you use the same camera (with appropriate filters) for visible-spectrum, IR with various cutoff frequencies and even (with some sensors anyway) UV photography.
You can certainly go for a shorter wavelength cutoff with your conversion too, like 720nm, and then use lens filters that cut at longer wavelengths below that for a stronger IR effect. I don't know of any problems in doing this other than the usual potential stuff associated with putting more glass surfaces between your subject and your sensor.
-Dave- (edit: removed double signature)