Too much is bad and can cause a leak in the seals.

I have a service manual here, it says 8 and 4. The hubs each hold a little less than 4 oz., therefore a 8oz bottle will do a little more than two hubs, maybe three.

 

8 and 4 is what my manual says too. Mine hold about 3 oz.

 

I've used synthetic atf in the hubs of my '03 SP500 since the first service. Over 2000 miles on it now and never a hub problem. I usually turn the fill hole up to a 2 o'clock position, fill the hub (using a small squirt-type oil can), then turn it down to 4 o'clock and let it drain to the proper level. I find that a little easier than trying to fill with the hole at 4 o'clock. One litre of synthetic atf is about 10 - 12 bucks in my area. Alot of fluid changes for a cheap price.

 

Is that 10-12 CDN or USD? I fill it up completely, then drain the excess also. I figure it helps get some of the old crap out of the hub.
Also, you can use the ATF fluid to "rinse" the hub out by changing it, ride in a circle, change it, ride in a circle, then fill it with real hub fluid. This helps clean it out if you had a lot of metal or water in there if you hadn't changed it in a while.