How do I download i-tunes directly to my 1Tb external hard drive?

Our external hard drive unit just died, taking my and my wife's i-tunes libraries with it.

When we bought the Mac desktop and the external HD unit from the Apple store, the staff transferred our i-tunes libraries from our

old pc to the external HD unit as we wished to keep the Mac HD clear of all the I-tunes data (I have over 1500 CDs and was slowly

adding these to my library, so it was quite a loss but mostly of time as I still have the CDs to copy again to my new library.) The staff

created separate libraries for my wife and I overnight so it was all done when we collected the machines from the shop, and I'd like to

re-create the separate libraries on the new i-tunes which we'll download from the Apple site. As there are no saved music tracks to be

moved, hopefully, the transfer won't take too long?

It seems we'll firstly have to download i-tunes to the desktop Mac and then transfer it across to the new HD unit, but I'd appreciate

some fool-proof straight forward instructions from anyone who can help - it is me we're talking about...... 😝. The new HD unit has been

formatted for Mac OS but that's all I've done so far.

Also, I have 2 ipods, my wife has one, and I was wondering if they'd still synch with the new libraries on the new HD unit, or would we

suffer the regular 'wipe-out' situation one reads about?

Cheers for any help.