As you have been told, in general counting on using your miles for upgrades is a losing game. In most airlines (even if MR/Capital one support transferring into their program), you can only upgrade the highest priced booking classes, *upgrade inventory permitting*. Using your points to book award tickets outright is a much better value, and gives you a guaranteed seat in the cabin class you want and saves you the disappointment of upgrade space scarcity, or waitlisted upgrade not clearing. Since you will quite likely have no frequent flier status with the airlines you'll try to upgrade, your upgrade request will be on the lowest rung of the upgrade pecking order. All other modes of upgrade involving cash, and all other upgrade requests by people with status, will quite likely go before you.

Not to mention that, by the time you book your flight in an upgradeable Economy booking class, it will likely not cost much more to book into a cheapest Business booking class.

Also, in general, always try to book directly with the airline, rather than an online travel agency like expedia or similar. It gives you more control over your booking, and in case of trouble, you will resolve it directly with the airline, rather than an intermediary. Of course, if you can find a good, trustworthy and reliable *actual* travel agent who will work in your best interest, that's the best option. But those are few and far inbetween.