Most universities will charge extra for using a credit card - keep in mind, they pay a fee to the card companies - and it is almost never worthwhile to pay the extra 2-3% fee to get rewards points. (Exception is if you need a relatively small amount to reach the threshold for a bonus, or need a relatively small number of points to redeem an award you want.)

Most people will get more points from signup bonuses than actual spending. (Yes, there are people who drops $000,000's or even $millions/year on CC's.) You could probably get the points needed to take your trip to LON and IST from two Citii AA cards (see the "two-browser trick"). UA and US also have cards with nice signup bonuses and no minumum spend (although US is less useful for a trip like yours, because you will only get 40K for signing up and they don't have one-way awards, so it's not like you can accumulate 30K or 40K or 50K and use them to go in one direction, then use a different carrier to go in the other.)

I know some of what I've said is a little cryptic, but the information is definitely all out there.