Thanks for the great response!
At the moment I am making simulations of all the major gravity assists done by for example Voyager I & II. I find it more convenient to use the concept of creating one Horizon file for one date then only create one simple system file which only includes date (which corresponds to the horizon file) and the wanted bodies. (Thanks Dan for updating the compability with that kind of files in future releases)
The bodies I am extracting from the Horizon database is all the planets with there corresponding major moons which is only the 4 largest of Jupiter, an 5 largest of Saturn for example, partially because all the moons was not discovered at that time plus the interesting man made space satellites at that time. (Is there some interest of extracting more bodies?)
I'll keep you updated Dan..