Welcome.
To be honest i did not find the 45mm PO to be that big, and i have a 7 1/2 inch wrist, the bracelet makes it heavy though, as long as the back is on tight and the crown is screwed down it should be fine in a shower but you would be better getting it checked first at you local mall watch battery change place. If you had a swiss movement and it was serviced it would last as long as you live (if serviced regualy) but that said asians can last a looooong time too. If you want a nice watch but dont want to spend a lot of cash the keep reading all the info is right here!