If it weren't for your location I'd say "You'll never get it to work, you might as well just give it to me to dispose of" ;-)
Steam jacketed kettles really let you do any time of brewing you desire. It is easy and simple to do a step mash so anything from there on down to extract is possible. But at 100L I would go all grain simply because the economics are going to be best in the long run (grain for that large of a batch is much cheaper than extract).