upgrade to C with Emirates?
 

I am planning to fly with my wife FRA-CMB in July OW, most convenient seems to be 1479 EUR in C, direct flight with UL. But when Y costs only 576 EUR and upgrade to C is 37500 miles, would it make sense for us to become Skywards members and buy 25000 miles today each +12500 miles next calendar year, cause it'd cost only 650 EUR so 1226 EUR altogether, saving 250 EUR per face.
Did I understand correctly, that I can buy miles before I've earned any miles flying with Emirates?
Also when and how should I ask for upgrade with miles? Or does this whole plan make sense at all?'
Also, do EK or UL have any business class offers from Europe too, sometimes, instead of having them all the time from CMB? :D

Yes you can. And is a good bang for your buck.
However if you are planning on doing the same/similar trip in the future, it could be more worthwhile flying in C, then using the miles you earn (7500+first flight bonus) for the next upgrade.

You could consider booking outbound in C, and when returning get the Y and upgrade; you will find fares from CMB are much cheaper than ex-FRA; just looking at it now, it quoted 1168US ow to FRA, and 442US ow in Y! (1836US return, and 705US in Y, which is what you are paying ow from FRA!).

Hope this helps.

I also suggest you give the trip as in whole, a good round of analysis (ie think for long term).