Hi Enzo,
I think you have a good idea. If you keep the Chunks entity non-persistent I think you will have absolutely no problems.
Otherwise, i.e. if you use persistent object you might notice slight memory problems, but only if the string is really big e.g. largere than 256*1000 =256 000 chatacters IOP.
Regardless of whuch type of entity you choose, there will probably be no time concerns. For most APIs it is ussually the case that time is mainly spent waiting for I/O.
hope this helps,
Andrej