yes, its going to be tucked!

How much would guess? Like a stock 19'' wheel?

pretty much like the OEM 19s. i also have a set of 20" wheels that had that OEM 19s look (when dropped). i have a set of 25mm spacers for sale. they are less than 2 weeks old, and i will let them go for $85 shipped.

here is the thread (check out the pics):
https://g35driver.com/forums/archived-sales/127702-fs-25mm-wheel-spacers-almost-new.html

Thats going to be pretty tucked.
My 8.5/9.5 combo is +25mm front and +20mm rear.

Stock is +30mm.

I am thinking about getting wheel spacers for them. Ideally I want there to be an aggressive gap. What size would make them flush?

I would go +25 all around and roll your fenders for the most aggressive look, since people have run 9.5+ 17/10.5 +18? 8.5+15 9.5+15 should work just fine with some rolling.

Sunken Battleship offsets.

Does anyone NOT recommend spacers? would 25mm spacers require fender rolling?

It will most likely require rolling in the rear, but if you want the flush look then thats what you are going to have to do

Would 20mm spacers clear? Is 15mm too small? Which one would be better?

20mm spacers might require fender rolling. 15mm should be fine for the front. Not sure about the rear. Search around for offsets that people have with your width of wheel.

Just buy rims with the right offset instead...

^ +1 - and you would also get more lip

*edit*
What wheels are you looking at getting anyway? I'm in your area, I could come by and test fit them on my SEDAN!

Most people on here dont like them, but I do...Tsw Thruxtons. Theyre on ebay right now, but he'll sell them local.