Big machines almost always have just one active (TE) block, the rest is decoration. So no need to limit them more than small ones.

I think people that will seriously play a lot and make it to really advanced stage will be the more mature ones, so something to measure load/lag in a chunk and a general rule about downsizing on admin request should be enough.

Also, I remember the official TnFC server (when it was still on) had a reset scheduled every 6(?) hours. There was a countdown from 10 minutes (10,5,1,30 sec, 15 sec, 10 sec, 5 sec, zero) so nobody was surprised when it happened. There were no limits on building stuff and at its peak the server had 10+ players active at the same time, some lag sometimes occurred, but nothing drastic. I suspect this setup was made to counteract poor garbage collecting behaviours.

I know some people will say restarts are a pain, but personally, if I had to choose between more strict limits or restarts, I would pick restarts.

As for the proposed rules, 3 plots don't mean 1024 blocks, it's 4 plots