Peter --
None of the measures you suggest will help protect your grid against being sued. If your users build a triangle on your grid, and some creator somewhere decides that they copybotted their copyrighted triangle and brought it to your grid, and you don't have a DMCA agent registered, they can sue you.
Or, what is more likely to happen, they will threaten to sue you unless you pay a "licensing fee" (which, in some cases, will be legitimate, and in other cases will simply be extortion). If you don't have the money to defend yourself in court, you might find it cheaper to settle.
Will the EFF and the FSF take on your case? If you're one of thousands of victims of such a scam, they might. If it's just you? Probably not.
Copyright trolls rarely go after the individual uploaders unless there are a large number of them -- for example, the record companies and movie companies used to go after teens sharing files (but seem to have scaled back after a wave of negative publicity and pushback in the courts).
If a legitimate content creator goes after an actual infringer, and it's a one-time, accidental thing, the copyright creator will usually be happy to get an apology and removal of their content.
The courts are usually only involved when there are potentially large sums of money at stake -- either a big infringing class, or a big fat corporate target. So if you're a company with a grid, and you have deep pockets -- or someone might think you have deep pockets -- DMCA registration is a no-brainer, and very, very very cheap insurance against these lawsuits.