Re: Best of luck...
"If the boffins at SpaceX even come close on this next mission, the next obvious step is possibly a sea based platform, then try for land."
I doubt it. Sea based platforms are expensive, whether custom-built or repurposed oil rigs. SeaLaunch won't want them within a thousand miles of Ocean Odyssey in case it goes bang, lands on the wrong bit of Odyssey, falls over when it lands or otherwise makes a mess of the place.
Drop it gently and precisely into the sea to prove you can, then move to a land site, which can amount to little more than a sodding great concrete pan in the middle of the desert with a road to truck it out - a hell of a lot cheaper to build than a sea platform and much less expensive to rebuild if you break it (how?), with nothing of value in the surrounding area if it all gets noisy!
One of SpaceX's cost cutting endeavours has been to launch from a pretty bare pad - roll the rocket out of a horizontal shed, tip it on end and light the blue touch paper. None of these massively expensive and very complex launch towers or service structures. They can pretty much go from anywhere with a bunker for Launch Control and a big fuel bowser, which makes logistics much simpler when you want to land a rocket on end in a wide open desert.
Of course that'll have to change when they go manned because the 'nauts will need to get up to the capsule at the pointy end (unless they load them in and then tip it up!?), but I don't see them building stuff like the Shuttle or Apollo service structures. Bare pads are cheap (relatively speaking) and they've designed the vehicles for them. No need for sea platforms and the like.