Hi from Canada and welcome to this rather eclectic collection of characters.
The most influential part in the sound production chain is the part behind the mouthpiece, then comes the mpce/reed, then the neck and finally the sax.
No matter what you do you will always sound like you. IMO the thing to work on first is the sound you make, as one gets closer to the sound one wants then one can tell what gear is making it harder to get your sound and what is making it easier. I think it is way too easy to get caught up in the gear search too early. Take it from someone who climbed that mountain, only to realize that the money being spent was premature.
Imo the first big change in gear should be to find a mpce whos characteristics assist in getting ones sound. Altos and sopranos are imo quite different from tenor in that they are higher pitched and smaller bores so a mpce style that works with tenor can often end up sounding a bit thin or shrill at first.
Advice unasked for etc etc but i suggest that if the gear bug is on you hard and fast, talk to some mpce guys like Morgan Frye on your side of the pond and try that. If there are technical issues around the alto, bad ergos sloppy or slow action, well then thats a different kettle of fish.
My .02 anyway.
Good luck