There is a thread around about the difficulties of adding a Type IX to SH5.
http://www.subsim.com/radioroom/showthread.php?t=233811
As far as I know, itīs impossible to add shadows and to see the hull below the waterline on imported ships. Wakes, damage models an so on are possible, but a heck of a work.
Hence respect for the great work that was done in TWOS.
Moreover Iīm not sure, if itīs possible to add as much .dats to SH5 as you want to or if at some point you will run into stability issues.
Would be interested in the answer too.