[G4] Need "handholding" while experimenting with OSX

[Sy]

I have a G4 running System 9.1.

Several weeks ago I explained here that I have very
old apps that work fine on 9.1 but surely won't run on
OSX.  I would like to try the OSX evironment but an
worried about screwing up my computer.

It  was suggested that I use an external HD (which is
about 80 GB in size ) load OSX onto that and boot from
that drive and "experiment" with OSX..  I would like
to have the OSX with the "Classic" feature because I'm
told this I will still be able to run my old apps that
way.

My questions are:

*Where do I get the OSX disc-From Apple?  Which one
Panther etc.?

*Because I will be booting the computer from this
external HD is there any chance it could screw up my
internal drive?

*Will using OSX screw up my Internet (cable modem)
settings or anything else (like peripherals) so that I
can't readily use them when I reboot from my internal
9.1 HD.

I have a knot in my stomach as I type this because
sometimes it's best to just "leave well enough alone",
but I want to try OSX.

Any advice willbe appreciated.

Thanks,

Sy