I did some "modeling" paper and pencil version, and if the footprint was 36" x 36" you could also use it as a tackling sled, and have a hard time knocking it over. Can you stand that sized footprint? I'm pretty sure 30 x 30 would work almost as well. So I think your sizing is just fine. For stuff like this I always overbuild, but generally I have plenty of room. I don't see it tipping, or being a tip hazard unless you cut the area it's on down significantly. 

I think Oneida's stands might be more tippy, just due to weight. Looks like they are trying to go ultra low weight, which I imagine is driven by shipping cost, so in this case building out of wood is going to anchor you better I believe. 

On my first DC roll around I made a double thick base. Used 2 sheets of plywood with a tuba4 frame. Inside the frame, and between the plywood I laid in a pattern of cheapazz paver blocks, simply for low low bottom weight. That sucker wasn't going to fall over EVER. Used a good quality 10" wheel and it tipped right up, and rolled wherever I wanted it to go. On my second one I started with just  a base of 1 sheet 3/4" plywood, it also worked well, so I just saved some time, but using the double base would guarantee anti tip, and at that point it wasn't really any difference to roll around, provided you have wheels up to the task.