Great looking choice, and another voter for Metzeler tires...I just switched to them and wish that I had done it a long time ago. Contact the folks at HogPro.com for your wheel questions. They are the most knowledgeable folks that I have come across, and good prices too!
What he said...talk to Phil at HogPro, tell him you are a CVO member and you'll get free hardware and shipping. I had them mount and assemble everything so wheels and tires came ready to put on.
The 150/70x18 will fit on rear without issue...you're not carrying a load on the FB, so the load rating shouldn't be an issue. The 4.25" wheel with that tire will look great. On front, I would go with a 3.5" wheel, 18" of course, and a 140/70x18 if you want to stay with 18's front and rear, and a fat tire look. You can put a 19 on front too. Talk to Phil, he's seen it all done...