Having never owned a Mac, I never knew it can do everything a PC can. (I must sound like a right old codger; but I'm not - HONESTLY! I've still got all my own hair!!!!) So a MacBook with Logic is looking good!
And good advice re transfering data from the 4416. Thanks.
So it looks like the one thing I'm still pondering is the "Mixer & interface or just super-duper interface" question...... Keep that advice coming. It's all good.