Horse stall mats seem to work well, a few of them that is.
You have stones already? You can also get a couple of tires with an outside diameter a little larger than the stone, and drop the stone on those.
Your deadlift isn't going to be the limiting factor when you begin attempting to lift stones, your technique on the pick will. The pick technique is something I have difficulty explaining. Stand over the stone, with your toes bisecting it. Clench your fists, and dig your forearms into the sides of the stone, with a slight slight bend. Your hips will shoot up, unlike a deadlift.
In terms of loading to a platform, You'll probably start with a two part pick/lap and load. Once you have lapped the stone, lay your arms over the top, pull it into your chest as high as possible, then push your hips through, roll it up your body, and load. With lighter stones, and as you get better, you can do a one motion pick and load.
For doing other events, just keep an eye on your recovery. If you need to, cycle between heavy and light SM training days, or you could even do some events light, some heavy on the same day to manage training load.