I've never made a proposal, so I don't know if the DHF allows the proposal maker to vote for their own project. Lasseehlers upvotes his posts but didn't upvote his proposal, so there is a possibility that isn't allowed. I'll need to find out how that works before I can knowledgeably respond to that point.

When you have millions of HP using another account to create the DHF isn't the main barrier.

What I think I might be able to say is that making a proposal may fall under contract law

It might, or might not never heard about that tbh.

It would be a simple brute force attack by just staking enough HP to cancel out all the upvotes for any new propoasal to impede the progress of our blockchain.

Well this would need a lot of HP, not sure it would even be possible to find enough hive on the market to suddently brute force. And even if highly immoral technically cutting the financement of all the hive project isn't illegal by unvoting all the proposal it's just voting for what ever you wish to be accepted. As long as you have the HP you have the right to vote/unvote what you want, unlike the witness thing with justin you don't earn from cutting the dhf pay.

I am just beginning to learn blockchain development

Not really related but, do you wanna become a blockchain dev like making your own chain or upgrading other chains or why are you learning ?