Wow - I think you may be our first owner in here from South Africa! Your plan sounds like a good one. Don't wait too long on getting the dry rock in - the sooner the better to get the bacteria established on it.
Edit - I see you posted live, not dead, rock. You may have a second cycle to go through if the future rock has any die-off. But, if the future corals come on large pieces of LR then no worries. Looking forward to more pictures!
I'd say most of us pulled out, or never put in, the ceramic media as the LR should be able to handle the cycle, and some tank manufacturers even recommend not using it in reef tanks (can be nitrate generators). Personally I'm not in favor of any rock in the back of these tanks as all it does is catch a lot of debris and generate nitrates. I once ran rubble in a bag in the back of my 130, to make it easy to pull out for rinsing, but that bag sure did catch a lot junk on it. Loose rock in back could be difficult to pull out. Just my opinion. I'm not sure about pulling the sponges out of the 250 - also can be nitrate generators if not rinsed often, but I think one of them is to trap bubbles?