[Alicia]

I love massaging in the shower, as you say it's easier, and also very pleasurable... in fact it makes me feel sexy (...and horny) So bad I can't spend too much time in the shower because people at home start knocking at the door telling me to get out lol. So 99% of the time I massage after the shower.
I'd say do it in the shower if you feel more comfortable, I don't think it won't create less pressure, in fact, whenever I massage in the shower I get the feeling I'm applying more pressure than I normally do, because as the breasts get so smooth and slippery *I think* they "adapt" to that pressure more easily, if you know what I mean (sorry, English isn't my 1st language, as you may have noticed lol)

As for massaging with the opposite hand, I don't know if anybody does it like that, but I think that if you can apply the same pressure and make the exact movements you would do if you were massaging normally it should be ok. I say this because I've tried doing it like that a few times but I've always ended up "pulling" the breast to the opposite side (I mean if I'm massaging my right breast with my left hand I would pull it to the left), unvoluntarily of course, and it hurt. But if you feel ok doing it that way then why not perhaps my arms are too short lol.