An expert? Gosh no. If i was i would not be in this situation!!!
If you select all the files in your lightroom catalogue, then you can goto
file+export as catalogue. Choose a destination (removable hd) and it'll copy all your files to the new location with the all important catalogue file. There is probably another step to put them on the new mac. My experience of mac is that when you set up the new one it will offer to basically clone your old machine onto your new one. Trick is to not delete your old one until your new one is happy and you and sure you have everything.