Optimal Offset and Size for Integra

I have a 95 Integra LS that I will be dropping a GS-R engine in soon. But anyway, I am looking into getting the Motegi Racing MR7. The site recommends I get 16's. And I know that this is probably the best choice for size and comfort and racing and so forth, but I want those 18's.

Stock offset for Integra is 45mm. The 18's have a offset of 40mm. Is this going to cause a problem? And if so, can I buy a 5mm spacer somewhere that could solve the problem?

I calculated the size of the wheel plus tire and it will be only 0.71" (1.8034 cm) taller than the current stock wheels/tires I have now. So I can tuck the 18's easily.

So, can I put 40mm offset tires into my Integra?

42-45mm is optimal if you don't plan on lower you can get away with 39-40mm.

But for lowering you can be confident not to rub with a 42-45mm Offset.

Are there spacers available to get the offset out a little farther?