Regarding #1, I agree with Johnson Lau and others who have responded since then—this proposal is not appropriate and should not be adopted for the following reasons:
1. Miners will view it as way too little, delivered way too late. And as soon as you say 300kb blocks, you've lost them all.
2. "Spam" - You're very fixated on this concept of spam transactions, but the transactions that you deem as spam are legitimate, fee-paying transactions. They're not a problem for miners. It's only a problem to you as you've arbitrarily decided some transactions are legit and some are not. It's an imaginary problem and we should focus on designs that solve real problems instead.
Also, even if you changed the max size to 300kb, transactions that you (and as far as I can tell, only you) consider spam will still be in there! They'll just be paying a ridiculous fee along with everyone else.
3. 17% per year growth rate - This is making the assumption that the current 1MB limit is already at the upper limit supportable by the network. This isn't even remotely true, and starting this rate at the current limit would cause the system to lag far behind the actual capability of the network for no reason.
4. Nodes - Individuals have no incentive to run full nodes and we've already passed the time where it makes any sense for them to do so. Therefore restricting the blockchain size in an attempt to keep individuals running nodes is futile at best and likely very damaging. Miners and businesses using Bitcoin do have an incentive to run nodes and over the years we've seen a migration of nodes from weak hands (individuals) to strong hands (businesses).
Overall, this proposal would hamstring Bitcoin Core and would drive miners towards Unlimited.
- t.k.