I ride western as well as english, Although i've never introduced a western saddle to a horse thats only been ridden english - The horses i rode were ridden english and then western though and seemed fine (One actually preferred the western).
Pros for me are;
Deeper securer seat - Great if you lack confidence
Synthetics especially are AMAZINGLY comfortable
Seemingly much more gentle when girthing them up (Judging by the horses reactions, have had horses who hate being girthed english but dont bat an eyelid western)
Seem to have less problems with oddly shaped horses and saddles slipping - never had a western slip
Cons;
That horn on the front fucking wails if you fall off and hit it - You can end up with a nastily bruised thigh from it. Obviously if your horse likes to stop dead too there is the risk of hitting it if you're not able to sit it back.
They can be expensive. We had a couple of leather ones and a couple of synthetics and tbh if you're just using it for riding about i would go for a synthetic, robinsons do a nice comfy one that i liked.
I don't find them too heavy, heavier than an english yes.
Do you actually want to learn to ride western? Or just ride in a western saddle? Western riding is nice. Or you can get a sort of middle ground between the two (I rode one mare in english bridle but western saddle, just far more relaxed with the reins than you would be in english normally, worked for us).