I throw my floss out weekly when i do my waterchanges. I only use a handful so a bag will last you quite a while.
I replace my phosban about every 3 months (just did it today actually). I have never heard about it releasing the phosphate back into your tank but will have to look into that.
The Maxijet 1200 is a better pump for a few reasons, the main one is reliability.
I did months of reserch before setting up my cube (Registered here in Dec. 05, didn't start the tank until April 06) and everyone was replacing the stock pumps with Maxijets 1200 so off the bat I did it. Kept the stock one around for mixing saltwater and it just crapped out on my about 2-3 weeks ago. That cheapo pump didn't even last a year with only 2-3 days of use a week. If that would have died on me overnight or when I was at work my tank would have crashed and everything would have died.
I can't really compare the maxijet 1200 to the stock pump inside the unit because I never used the stock pump but I can say the 1200 does a real good job. I upgraded my lights recently and got some gorgs and other high flow needing corals so I have a maxijet 600 in there now as well. need to figure out a way to plumb it in for the long term.
And I do run a lot of chemical media but I also keep a lot of fish and a ton of corals (Up until last Monday I had 6 fish, one being a good sized flame angel, the flame angel just died last monday though so I'm back to 5 until I get my Onyx Clown in on Thursday). I also have a good deal of softies/LPS mix. LPS hates the chemicals that softie's can put off and if I want to avoid chemical warfare with the corals I need all the media I can get.
I first added phosban for cyano and just never stopped using it, I wouldn't bother with it unless you get a cyano outbreak, it's totally not needed at the start of a tank.