Nylon strings may not sound very good on a guitar designed for
steel strings. That said, you may be able to find ball-end nylon strings that may get you at least a little closer. However, you'll need to get your nut re-slotted to accommodate the wider nylon strings.
As far as a 7th string goes, that might be more difficult. What i would do is find out the gauge differential between the 5th and 6th strings, then add that to the 6th string gauge to get an approximation of where you should be for the 7th string.
Good luck! I'm sure many people will be interested to know how it turns out.