I used to work over at Windward Honda, just go there ask for Mel Ramos one of the desk managers, and tell him Earl sent you there and he will help you get the car at you want, message me if you need more help
Front is 19x8.5 +40 with 235/35/19, rear is 19x9.5 +35 with 255/30/19 lowered on Eibach sport lines, been running this setup for about 3 years with minor rubbing, I will be addressing that real soon here
This is 19x9.5 +35 with 255/30/19 rear, 19x8.5 +40 with 235/35/19 front just for reference, it does rub with a full load only on bumps, but I will roll the fenders to stop that, I am running eibach sport line springs
You totally can do this, when I got mine, I pulled out the sockets from both mirrors and used a jack, put the face on a block of wood and jacked it up under my truck and just snapped the ball into the socket, there are risks though, just go slow
Offset is the spacing from hub mating surface to rear of rim, that does not change weather it is 18" or 19" your +30 is just more aggressive than my front which is +40 and still more than my rear which is +35