Maybe we need to define "doubling opportunities" here.
If we assume it to mean "playing a second instrument in a big band", then I agree that opportunities are few - although I did use my alto flute with big band. It is actually quite good to use alto flute when the written parts are voiced so low as to not have much volume.
On the other hand, if you are the wind player in a small ensemble, you are not constrained in your selection.
Alto flute - It's the tenor sax of the flute world.
I did assume "doubling" as in big band or pit work.
In my experience it's really hard to hear the alto except in a quiet ensemble. In other words, if you've got a grand piano, electric bass, drums, two trumpets and a tenor sax, the alto flute is going to disappear without significant amplification. If you have two acoustic guitars and upright bass playing bossa nova, there will be nothing more beautiful than alto flute. (In fact, just writing that makes me want to find a couple guitar players and get started.)
OP, another issue is that you have to decide between curved and straight head. Personally as a long time flute player, male, of average stature with long arms, the straight is workable and seemed to sound a bit better; but if you have short arms or bad shoulders you may want to consider the curved head.
As I noted above, I'm not sure whether it's possible or advisable to start on alto flute. I'm sure it's quite rare to do so, given how many flute players there are and how few alto flutes there are; but I don't think that means you HAVE to start on alto flute. It might be worth going to one of the flute message boards ("Fluteland"?) and asking that question. We have had, here on the saxophone forum, questions like "can I start out on baritone sax" and the consensus seems to be that if you're physically big enough to do it, there's no real good reason you can't start out on baritone sax. So I'm not convinced you would NEED to start out on C flute.