Well in the end my wife and I had around 14 mules (14 extra bucks on our monthly bill) just trying to keep things straight. I had several jobs at 30 and 40 and some at 50 as well as a 75 Bard, which was decked out beyond belief both at 75 and at all caps. She had 3 level 75 jobs decked out.
Many of our mules were simply gear storage. Capped gear for our mains and for other jobs. I had an entire mule dedicated completely to my Bard's gear as well as one for all of my melee jobs and another for all of my mage jobs. Beside that, it's great to have a mule in each city so you can have access to all of the Auction Houses at a moments notice and sell (or buy) things quickly and easily where the market is good.
One of the primary ways we manage to make money without stopping too often was to simply keep ALL of the random drops we got and sort them to be sold among our mules. A lot of people keep mules for gardening as well since it can make a lot of money. The number of AH slots you can use is 7. So if you went mining or something and wanted to sell a lot of stuff, it could be backed up in your box for well over a week unless you sent it to a mule to be taken care of.
SE keeps adding storage mediums, and this is great, but it's just not enough. Most people I know with multiple jobs just end up playing one gimp by sharing gear that is only marginally useful simply so they don't have to use that much more inventory space.