HeHe...Sorry to laugh, but you guys crack me up with the whole bioball thing.....I know how you feel though, I thought the LFS guy was a moron when he said to get rid of them!!! Trust me, it'll be fine. As far as the "space in the sump" why do you need anything there? A filter is sock is basically what it sounds like, it looks like a sock and acts like a filter. What you need to realize is that any kind of filter (sock, floss, sponge, etc.) will filter mechanical debris, but will also be a bacteria breeding ground like the bioballs (which you're trying to get rid of) so whatever you choose to do, keep it clean.
The question about the sump....The sump does a lot. It let's you get stuff out of the main tank (heaters,pumps,blablabla), it acts as a reservoir that increases your total volume of water, gives a place to safely add chemicals, increases the oxygenation and movement of H2O, and all kinds of good stuff. Do you have to spend hundreds of dollars on it? NO!! You can make one from a rubber-maid box!! All it really is, is a box that holds water!!! Do some research and see what you find.
I'm gonna recommend that all of you check out Melev's reefsite, he has a ton of info in simple terms and explains a lot.
Someone posted before about low pH problems. 450 may be little high on the Ca. I think the alk was like 3.5, I'm guessing that's in dKh values, and that's way to low for a reef. You need to add some baking soda (NOT baking powder). This will increase your bicarbonate levels (Increase pH-more alkaline, but it will also bind to Ca to produce calcium carbonate, so you need to watch your Ca levels while making this adjustment). Do a google search for "marine aquarium calculator" and you'll get to a webpage that gives you calculations for additives based on tank size and current levels. Add whatever it tells you, but spread it out over a couple of days, also, don't dose Ca and the baking soda on the same day, or if you do, spread it out 'cause they will rapidly bind and you'll have a snowy effect in the tank for a day or 2 (been there, done that!!).
As far as the DSB bucket idea, it sounds great, but do you really need it? I've never even really heard of anyone using one, and it seems like a project that might be cool, but might also just eat up some time and money. your money may be better spent on more LR or livestock.....Just my opinion. Hope this helps, post some more if you have other questions and don't forget to check the forums, magazines online, and google for info, there's tons of info out there.